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CommitLineData
1da177e4
LT
1/*
2 * Fast Userspace Mutexes (which I call "Futexes!").
3 * (C) Rusty Russell, IBM 2002
4 *
5 * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
6 * (C) Copyright 2003 Red Hat Inc, All Rights Reserved
7 *
8 * Removed page pinning, fix privately mapped COW pages and other cleanups
9 * (C) Copyright 2003, 2004 Jamie Lokier
10 *
0771dfef
IM
11 * Robust futex support started by Ingo Molnar
12 * (C) Copyright 2006 Red Hat Inc, All Rights Reserved
13 * Thanks to Thomas Gleixner for suggestions, analysis and fixes.
14 *
c87e2837
IM
15 * PI-futex support started by Ingo Molnar and Thomas Gleixner
16 * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
17 * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
18 *
34f01cc1
ED
19 * PRIVATE futexes by Eric Dumazet
20 * Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
21 *
52400ba9
DH
22 * Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
23 * Copyright (C) IBM Corporation, 2009
24 * Thanks to Thomas Gleixner for conceptual design and careful reviews.
25 *
1da177e4
LT
26 * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
27 * enough at me, Linus for the original (flawed) idea, Matthew
28 * Kirkwood for proof-of-concept implementation.
29 *
30 * "The futexes are also cursed."
31 * "But they come in a choice of three flavours!"
32 *
33 * This program is free software; you can redistribute it and/or modify
34 * it under the terms of the GNU General Public License as published by
35 * the Free Software Foundation; either version 2 of the License, or
36 * (at your option) any later version.
37 *
38 * This program is distributed in the hope that it will be useful,
39 * but WITHOUT ANY WARRANTY; without even the implied warranty of
40 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
41 * GNU General Public License for more details.
42 *
43 * You should have received a copy of the GNU General Public License
44 * along with this program; if not, write to the Free Software
45 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
46 */
47#include <linux/slab.h>
48#include <linux/poll.h>
49#include <linux/fs.h>
50#include <linux/file.h>
51#include <linux/jhash.h>
52#include <linux/init.h>
53#include <linux/futex.h>
54#include <linux/mount.h>
55#include <linux/pagemap.h>
56#include <linux/syscalls.h>
7ed20e1a 57#include <linux/signal.h>
9984de1a 58#include <linux/export.h>
fd5eea42 59#include <linux/magic.h>
b488893a
PE
60#include <linux/pid.h>
61#include <linux/nsproxy.h>
bdbb776f 62#include <linux/ptrace.h>
8bd75c77 63#include <linux/sched/rt.h>
13d60f4b 64#include <linux/hugetlb.h>
88c8004f 65#include <linux/freezer.h>
a52b89eb 66#include <linux/bootmem.h>
b488893a 67
4732efbe 68#include <asm/futex.h>
1da177e4 69
1696a8be 70#include "locking/rtmutex_common.h"
c87e2837 71
99b60ce6
TG
72/*
73 * Basic futex operation and ordering guarantees:
74 *
75 * The waiter reads the futex value in user space and calls
76 * futex_wait(). This function computes the hash bucket and acquires
77 * the hash bucket lock. After that it reads the futex user space value
b0c29f79
DB
78 * again and verifies that the data has not changed. If it has not changed
79 * it enqueues itself into the hash bucket, releases the hash bucket lock
80 * and schedules.
99b60ce6
TG
81 *
82 * The waker side modifies the user space value of the futex and calls
b0c29f79
DB
83 * futex_wake(). This function computes the hash bucket and acquires the
84 * hash bucket lock. Then it looks for waiters on that futex in the hash
85 * bucket and wakes them.
99b60ce6 86 *
b0c29f79
DB
87 * In futex wake up scenarios where no tasks are blocked on a futex, taking
88 * the hb spinlock can be avoided and simply return. In order for this
89 * optimization to work, ordering guarantees must exist so that the waiter
90 * being added to the list is acknowledged when the list is concurrently being
91 * checked by the waker, avoiding scenarios like the following:
99b60ce6
TG
92 *
93 * CPU 0 CPU 1
94 * val = *futex;
95 * sys_futex(WAIT, futex, val);
96 * futex_wait(futex, val);
97 * uval = *futex;
98 * *futex = newval;
99 * sys_futex(WAKE, futex);
100 * futex_wake(futex);
101 * if (queue_empty())
102 * return;
103 * if (uval == val)
104 * lock(hash_bucket(futex));
105 * queue();
106 * unlock(hash_bucket(futex));
107 * schedule();
108 *
109 * This would cause the waiter on CPU 0 to wait forever because it
110 * missed the transition of the user space value from val to newval
111 * and the waker did not find the waiter in the hash bucket queue.
99b60ce6 112 *
b0c29f79
DB
113 * The correct serialization ensures that a waiter either observes
114 * the changed user space value before blocking or is woken by a
115 * concurrent waker:
116 *
117 * CPU 0 CPU 1
99b60ce6
TG
118 * val = *futex;
119 * sys_futex(WAIT, futex, val);
120 * futex_wait(futex, val);
b0c29f79
DB
121 *
122 * waiters++;
123 * mb(); (A) <-- paired with -.
124 * |
125 * lock(hash_bucket(futex)); |
126 * |
127 * uval = *futex; |
128 * | *futex = newval;
129 * | sys_futex(WAKE, futex);
130 * | futex_wake(futex);
131 * |
132 * `-------> mb(); (B)
99b60ce6 133 * if (uval == val)
b0c29f79 134 * queue();
99b60ce6 135 * unlock(hash_bucket(futex));
b0c29f79
DB
136 * schedule(); if (waiters)
137 * lock(hash_bucket(futex));
138 * wake_waiters(futex);
139 * unlock(hash_bucket(futex));
140 *
141 * Where (A) orders the waiters increment and the futex value read -- this
142 * is guaranteed by the head counter in the hb spinlock; and where (B)
143 * orders the write to futex and the waiters read -- this is done by the
144 * barriers in get_futex_key_refs(), through either ihold or atomic_inc,
145 * depending on the futex type.
146 *
147 * This yields the following case (where X:=waiters, Y:=futex):
148 *
149 * X = Y = 0
150 *
151 * w[X]=1 w[Y]=1
152 * MB MB
153 * r[Y]=y r[X]=x
154 *
155 * Which guarantees that x==0 && y==0 is impossible; which translates back into
156 * the guarantee that we cannot both miss the futex variable change and the
157 * enqueue.
99b60ce6
TG
158 */
159
a0c1e907
TG
160int __read_mostly futex_cmpxchg_enabled;
161
b41277dc
DH
162/*
163 * Futex flags used to encode options to functions and preserve them across
164 * restarts.
165 */
166#define FLAGS_SHARED 0x01
167#define FLAGS_CLOCKRT 0x02
168#define FLAGS_HAS_TIMEOUT 0x04
169
c87e2837
IM
170/*
171 * Priority Inheritance state:
172 */
173struct futex_pi_state {
174 /*
175 * list of 'owned' pi_state instances - these have to be
176 * cleaned up in do_exit() if the task exits prematurely:
177 */
178 struct list_head list;
179
180 /*
181 * The PI object:
182 */
183 struct rt_mutex pi_mutex;
184
185 struct task_struct *owner;
186 atomic_t refcount;
187
188 union futex_key key;
189};
190
d8d88fbb
DH
191/**
192 * struct futex_q - The hashed futex queue entry, one per waiting task
fb62db2b 193 * @list: priority-sorted list of tasks waiting on this futex
d8d88fbb
DH
194 * @task: the task waiting on the futex
195 * @lock_ptr: the hash bucket lock
196 * @key: the key the futex is hashed on
197 * @pi_state: optional priority inheritance state
198 * @rt_waiter: rt_waiter storage for use with requeue_pi
199 * @requeue_pi_key: the requeue_pi target futex key
200 * @bitset: bitset for the optional bitmasked wakeup
201 *
202 * We use this hashed waitqueue, instead of a normal wait_queue_t, so
1da177e4
LT
203 * we can wake only the relevant ones (hashed queues may be shared).
204 *
205 * A futex_q has a woken state, just like tasks have TASK_RUNNING.
ec92d082 206 * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
fb62db2b 207 * The order of wakeup is always to make the first condition true, then
d8d88fbb
DH
208 * the second.
209 *
210 * PI futexes are typically woken before they are removed from the hash list via
211 * the rt_mutex code. See unqueue_me_pi().
1da177e4
LT
212 */
213struct futex_q {
ec92d082 214 struct plist_node list;
1da177e4 215
d8d88fbb 216 struct task_struct *task;
1da177e4 217 spinlock_t *lock_ptr;
1da177e4 218 union futex_key key;
c87e2837 219 struct futex_pi_state *pi_state;
52400ba9 220 struct rt_mutex_waiter *rt_waiter;
84bc4af5 221 union futex_key *requeue_pi_key;
cd689985 222 u32 bitset;
1da177e4
LT
223};
224
5bdb05f9
DH
225static const struct futex_q futex_q_init = {
226 /* list gets initialized in queue_me()*/
227 .key = FUTEX_KEY_INIT,
228 .bitset = FUTEX_BITSET_MATCH_ANY
229};
230
1da177e4 231/*
b2d0994b
DH
232 * Hash buckets are shared by all the futex_keys that hash to the same
233 * location. Each key may have multiple futex_q structures, one for each task
234 * waiting on a futex.
1da177e4
LT
235 */
236struct futex_hash_bucket {
ec92d082
PP
237 spinlock_t lock;
238 struct plist_head chain;
a52b89eb 239} ____cacheline_aligned_in_smp;
1da177e4 240
a52b89eb
DB
241static unsigned long __read_mostly futex_hashsize;
242
243static struct futex_hash_bucket *futex_queues;
1da177e4 244
b0c29f79
DB
245static inline void futex_get_mm(union futex_key *key)
246{
247 atomic_inc(&key->private.mm->mm_count);
248 /*
249 * Ensure futex_get_mm() implies a full barrier such that
250 * get_futex_key() implies a full barrier. This is relied upon
251 * as full barrier (B), see the ordering comment above.
252 */
253 smp_mb__after_atomic_inc();
254}
255
256static inline bool hb_waiters_pending(struct futex_hash_bucket *hb)
257{
258#ifdef CONFIG_SMP
259 /*
260 * Tasks trying to enter the critical region are most likely
261 * potential waiters that will be added to the plist. Ensure
262 * that wakers won't miss to-be-slept tasks in the window between
263 * the wait call and the actual plist_add.
264 */
265 if (spin_is_locked(&hb->lock))
266 return true;
267 smp_rmb(); /* Make sure we check the lock state first */
268
269 return !plist_head_empty(&hb->chain);
270#else
271 return true;
272#endif
273}
274
1da177e4
LT
275/*
276 * We hash on the keys returned from get_futex_key (see below).
277 */
278static struct futex_hash_bucket *hash_futex(union futex_key *key)
279{
280 u32 hash = jhash2((u32*)&key->both.word,
281 (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
282 key->both.offset);
a52b89eb 283 return &futex_queues[hash & (futex_hashsize - 1)];
1da177e4
LT
284}
285
286/*
287 * Return 1 if two futex_keys are equal, 0 otherwise.
288 */
289static inline int match_futex(union futex_key *key1, union futex_key *key2)
290{
2bc87203
DH
291 return (key1 && key2
292 && key1->both.word == key2->both.word
1da177e4
LT
293 && key1->both.ptr == key2->both.ptr
294 && key1->both.offset == key2->both.offset);
295}
296
38d47c1b
PZ
297/*
298 * Take a reference to the resource addressed by a key.
299 * Can be called while holding spinlocks.
300 *
301 */
302static void get_futex_key_refs(union futex_key *key)
303{
304 if (!key->both.ptr)
305 return;
306
307 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
308 case FUT_OFF_INODE:
b0c29f79 309 ihold(key->shared.inode); /* implies MB (B) */
38d47c1b
PZ
310 break;
311 case FUT_OFF_MMSHARED:
b0c29f79 312 futex_get_mm(key); /* implies MB (B) */
38d47c1b
PZ
313 break;
314 }
315}
316
317/*
318 * Drop a reference to the resource addressed by a key.
319 * The hash bucket spinlock must not be held.
320 */
321static void drop_futex_key_refs(union futex_key *key)
322{
90621c40
DH
323 if (!key->both.ptr) {
324 /* If we're here then we tried to put a key we failed to get */
325 WARN_ON_ONCE(1);
38d47c1b 326 return;
90621c40 327 }
38d47c1b
PZ
328
329 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
330 case FUT_OFF_INODE:
331 iput(key->shared.inode);
332 break;
333 case FUT_OFF_MMSHARED:
334 mmdrop(key->private.mm);
335 break;
336 }
337}
338
34f01cc1 339/**
d96ee56c
DH
340 * get_futex_key() - Get parameters which are the keys for a futex
341 * @uaddr: virtual address of the futex
342 * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
343 * @key: address where result is stored.
9ea71503
SB
344 * @rw: mapping needs to be read/write (values: VERIFY_READ,
345 * VERIFY_WRITE)
34f01cc1 346 *
6c23cbbd
RD
347 * Return: a negative error code or 0
348 *
34f01cc1 349 * The key words are stored in *key on success.
1da177e4 350 *
6131ffaa 351 * For shared mappings, it's (page->index, file_inode(vma->vm_file),
1da177e4
LT
352 * offset_within_page). For private mappings, it's (uaddr, current->mm).
353 * We can usually work out the index without swapping in the page.
354 *
b2d0994b 355 * lock_page() might sleep, the caller should not hold a spinlock.
1da177e4 356 */
64d1304a 357static int
9ea71503 358get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
1da177e4 359{
e2970f2f 360 unsigned long address = (unsigned long)uaddr;
1da177e4 361 struct mm_struct *mm = current->mm;
a5b338f2 362 struct page *page, *page_head;
9ea71503 363 int err, ro = 0;
1da177e4
LT
364
365 /*
366 * The futex address must be "naturally" aligned.
367 */
e2970f2f 368 key->both.offset = address % PAGE_SIZE;
34f01cc1 369 if (unlikely((address % sizeof(u32)) != 0))
1da177e4 370 return -EINVAL;
e2970f2f 371 address -= key->both.offset;
1da177e4 372
5cdec2d8
LT
373 if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
374 return -EFAULT;
375
34f01cc1
ED
376 /*
377 * PROCESS_PRIVATE futexes are fast.
378 * As the mm cannot disappear under us and the 'key' only needs
379 * virtual address, we dont even have to find the underlying vma.
380 * Note : We do have to check 'uaddr' is a valid user address,
381 * but access_ok() should be faster than find_vma()
382 */
383 if (!fshared) {
34f01cc1
ED
384 key->private.mm = mm;
385 key->private.address = address;
b0c29f79 386 get_futex_key_refs(key); /* implies MB (B) */
34f01cc1
ED
387 return 0;
388 }
1da177e4 389
38d47c1b 390again:
7485d0d3 391 err = get_user_pages_fast(address, 1, 1, &page);
9ea71503
SB
392 /*
393 * If write access is not required (eg. FUTEX_WAIT), try
394 * and get read-only access.
395 */
396 if (err == -EFAULT && rw == VERIFY_READ) {
397 err = get_user_pages_fast(address, 1, 0, &page);
398 ro = 1;
399 }
38d47c1b
PZ
400 if (err < 0)
401 return err;
9ea71503
SB
402 else
403 err = 0;
38d47c1b 404
a5b338f2
AA
405#ifdef CONFIG_TRANSPARENT_HUGEPAGE
406 page_head = page;
407 if (unlikely(PageTail(page))) {
38d47c1b 408 put_page(page);
a5b338f2
AA
409 /* serialize against __split_huge_page_splitting() */
410 local_irq_disable();
f12d5bfc 411 if (likely(__get_user_pages_fast(address, 1, !ro, &page) == 1)) {
a5b338f2
AA
412 page_head = compound_head(page);
413 /*
414 * page_head is valid pointer but we must pin
415 * it before taking the PG_lock and/or
416 * PG_compound_lock. The moment we re-enable
417 * irqs __split_huge_page_splitting() can
418 * return and the head page can be freed from
419 * under us. We can't take the PG_lock and/or
420 * PG_compound_lock on a page that could be
421 * freed from under us.
422 */
423 if (page != page_head) {
424 get_page(page_head);
425 put_page(page);
426 }
427 local_irq_enable();
428 } else {
429 local_irq_enable();
430 goto again;
431 }
432 }
433#else
434 page_head = compound_head(page);
435 if (page != page_head) {
436 get_page(page_head);
437 put_page(page);
438 }
439#endif
440
441 lock_page(page_head);
e6780f72
HD
442
443 /*
444 * If page_head->mapping is NULL, then it cannot be a PageAnon
445 * page; but it might be the ZERO_PAGE or in the gate area or
446 * in a special mapping (all cases which we are happy to fail);
447 * or it may have been a good file page when get_user_pages_fast
448 * found it, but truncated or holepunched or subjected to
449 * invalidate_complete_page2 before we got the page lock (also
450 * cases which we are happy to fail). And we hold a reference,
451 * so refcount care in invalidate_complete_page's remove_mapping
452 * prevents drop_caches from setting mapping to NULL beneath us.
453 *
454 * The case we do have to guard against is when memory pressure made
455 * shmem_writepage move it from filecache to swapcache beneath us:
456 * an unlikely race, but we do need to retry for page_head->mapping.
457 */
a5b338f2 458 if (!page_head->mapping) {
e6780f72 459 int shmem_swizzled = PageSwapCache(page_head);
a5b338f2
AA
460 unlock_page(page_head);
461 put_page(page_head);
e6780f72
HD
462 if (shmem_swizzled)
463 goto again;
464 return -EFAULT;
38d47c1b 465 }
1da177e4
LT
466
467 /*
468 * Private mappings are handled in a simple way.
469 *
470 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
471 * it's a read-only handle, it's expected that futexes attach to
38d47c1b 472 * the object not the particular process.
1da177e4 473 */
a5b338f2 474 if (PageAnon(page_head)) {
9ea71503
SB
475 /*
476 * A RO anonymous page will never change and thus doesn't make
477 * sense for futex operations.
478 */
479 if (ro) {
480 err = -EFAULT;
481 goto out;
482 }
483
38d47c1b 484 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
1da177e4 485 key->private.mm = mm;
e2970f2f 486 key->private.address = address;
38d47c1b
PZ
487 } else {
488 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
a5b338f2 489 key->shared.inode = page_head->mapping->host;
13d60f4b 490 key->shared.pgoff = basepage_index(page);
1da177e4
LT
491 }
492
b0c29f79 493 get_futex_key_refs(key); /* implies MB (B) */
1da177e4 494
9ea71503 495out:
a5b338f2
AA
496 unlock_page(page_head);
497 put_page(page_head);
9ea71503 498 return err;
1da177e4
LT
499}
500
ae791a2d 501static inline void put_futex_key(union futex_key *key)
1da177e4 502{
38d47c1b 503 drop_futex_key_refs(key);
1da177e4
LT
504}
505
d96ee56c
DH
506/**
507 * fault_in_user_writeable() - Fault in user address and verify RW access
d0725992
TG
508 * @uaddr: pointer to faulting user space address
509 *
510 * Slow path to fixup the fault we just took in the atomic write
511 * access to @uaddr.
512 *
fb62db2b 513 * We have no generic implementation of a non-destructive write to the
d0725992
TG
514 * user address. We know that we faulted in the atomic pagefault
515 * disabled section so we can as well avoid the #PF overhead by
516 * calling get_user_pages() right away.
517 */
518static int fault_in_user_writeable(u32 __user *uaddr)
519{
722d0172
AK
520 struct mm_struct *mm = current->mm;
521 int ret;
522
523 down_read(&mm->mmap_sem);
2efaca92
BH
524 ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
525 FAULT_FLAG_WRITE);
722d0172
AK
526 up_read(&mm->mmap_sem);
527
d0725992
TG
528 return ret < 0 ? ret : 0;
529}
530
4b1c486b
DH
531/**
532 * futex_top_waiter() - Return the highest priority waiter on a futex
d96ee56c
DH
533 * @hb: the hash bucket the futex_q's reside in
534 * @key: the futex key (to distinguish it from other futex futex_q's)
4b1c486b
DH
535 *
536 * Must be called with the hb lock held.
537 */
538static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
539 union futex_key *key)
540{
541 struct futex_q *this;
542
543 plist_for_each_entry(this, &hb->chain, list) {
544 if (match_futex(&this->key, key))
545 return this;
546 }
547 return NULL;
548}
549
37a9d912
ML
550static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
551 u32 uval, u32 newval)
36cf3b5c 552{
37a9d912 553 int ret;
36cf3b5c
TG
554
555 pagefault_disable();
37a9d912 556 ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
36cf3b5c
TG
557 pagefault_enable();
558
37a9d912 559 return ret;
36cf3b5c
TG
560}
561
562static int get_futex_value_locked(u32 *dest, u32 __user *from)
1da177e4
LT
563{
564 int ret;
565
a866374a 566 pagefault_disable();
e2970f2f 567 ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
a866374a 568 pagefault_enable();
1da177e4
LT
569
570 return ret ? -EFAULT : 0;
571}
572
c87e2837
IM
573
574/*
575 * PI code:
576 */
577static int refill_pi_state_cache(void)
578{
579 struct futex_pi_state *pi_state;
580
581 if (likely(current->pi_state_cache))
582 return 0;
583
4668edc3 584 pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
c87e2837
IM
585
586 if (!pi_state)
587 return -ENOMEM;
588
c87e2837
IM
589 INIT_LIST_HEAD(&pi_state->list);
590 /* pi_mutex gets initialized later */
591 pi_state->owner = NULL;
592 atomic_set(&pi_state->refcount, 1);
38d47c1b 593 pi_state->key = FUTEX_KEY_INIT;
c87e2837
IM
594
595 current->pi_state_cache = pi_state;
596
597 return 0;
598}
599
600static struct futex_pi_state * alloc_pi_state(void)
601{
602 struct futex_pi_state *pi_state = current->pi_state_cache;
603
604 WARN_ON(!pi_state);
605 current->pi_state_cache = NULL;
606
607 return pi_state;
608}
609
610static void free_pi_state(struct futex_pi_state *pi_state)
611{
612 if (!atomic_dec_and_test(&pi_state->refcount))
613 return;
614
615 /*
616 * If pi_state->owner is NULL, the owner is most probably dying
617 * and has cleaned up the pi_state already
618 */
619 if (pi_state->owner) {
1d615482 620 raw_spin_lock_irq(&pi_state->owner->pi_lock);
c87e2837 621 list_del_init(&pi_state->list);
1d615482 622 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
c87e2837
IM
623
624 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
625 }
626
627 if (current->pi_state_cache)
628 kfree(pi_state);
629 else {
630 /*
631 * pi_state->list is already empty.
632 * clear pi_state->owner.
633 * refcount is at 0 - put it back to 1.
634 */
635 pi_state->owner = NULL;
636 atomic_set(&pi_state->refcount, 1);
637 current->pi_state_cache = pi_state;
638 }
639}
640
641/*
642 * Look up the task based on what TID userspace gave us.
643 * We dont trust it.
644 */
645static struct task_struct * futex_find_get_task(pid_t pid)
646{
647 struct task_struct *p;
648
d359b549 649 rcu_read_lock();
228ebcbe 650 p = find_task_by_vpid(pid);
7a0ea09a
MH
651 if (p)
652 get_task_struct(p);
a06381fe 653
d359b549 654 rcu_read_unlock();
c87e2837
IM
655
656 return p;
657}
658
659/*
660 * This task is holding PI mutexes at exit time => bad.
661 * Kernel cleans up PI-state, but userspace is likely hosed.
662 * (Robust-futex cleanup is separate and might save the day for userspace.)
663 */
664void exit_pi_state_list(struct task_struct *curr)
665{
c87e2837
IM
666 struct list_head *next, *head = &curr->pi_state_list;
667 struct futex_pi_state *pi_state;
627371d7 668 struct futex_hash_bucket *hb;
38d47c1b 669 union futex_key key = FUTEX_KEY_INIT;
c87e2837 670
a0c1e907
TG
671 if (!futex_cmpxchg_enabled)
672 return;
c87e2837
IM
673 /*
674 * We are a ZOMBIE and nobody can enqueue itself on
675 * pi_state_list anymore, but we have to be careful
627371d7 676 * versus waiters unqueueing themselves:
c87e2837 677 */
1d615482 678 raw_spin_lock_irq(&curr->pi_lock);
c87e2837
IM
679 while (!list_empty(head)) {
680
681 next = head->next;
682 pi_state = list_entry(next, struct futex_pi_state, list);
683 key = pi_state->key;
627371d7 684 hb = hash_futex(&key);
1d615482 685 raw_spin_unlock_irq(&curr->pi_lock);
c87e2837 686
c87e2837
IM
687 spin_lock(&hb->lock);
688
1d615482 689 raw_spin_lock_irq(&curr->pi_lock);
627371d7
IM
690 /*
691 * We dropped the pi-lock, so re-check whether this
692 * task still owns the PI-state:
693 */
c87e2837
IM
694 if (head->next != next) {
695 spin_unlock(&hb->lock);
696 continue;
697 }
698
c87e2837 699 WARN_ON(pi_state->owner != curr);
627371d7
IM
700 WARN_ON(list_empty(&pi_state->list));
701 list_del_init(&pi_state->list);
c87e2837 702 pi_state->owner = NULL;
1d615482 703 raw_spin_unlock_irq(&curr->pi_lock);
c87e2837
IM
704
705 rt_mutex_unlock(&pi_state->pi_mutex);
706
707 spin_unlock(&hb->lock);
708
1d615482 709 raw_spin_lock_irq(&curr->pi_lock);
c87e2837 710 }
1d615482 711 raw_spin_unlock_irq(&curr->pi_lock);
c87e2837
IM
712}
713
714static int
d0aa7a70
PP
715lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
716 union futex_key *key, struct futex_pi_state **ps)
c87e2837
IM
717{
718 struct futex_pi_state *pi_state = NULL;
719 struct futex_q *this, *next;
c87e2837 720 struct task_struct *p;
778e9a9c 721 pid_t pid = uval & FUTEX_TID_MASK;
c87e2837 722
0d00c7b2 723 plist_for_each_entry_safe(this, next, &hb->chain, list) {
d0aa7a70 724 if (match_futex(&this->key, key)) {
c87e2837
IM
725 /*
726 * Another waiter already exists - bump up
727 * the refcount and return its pi_state:
728 */
729 pi_state = this->pi_state;
06a9ec29 730 /*
fb62db2b 731 * Userspace might have messed up non-PI and PI futexes
06a9ec29
TG
732 */
733 if (unlikely(!pi_state))
734 return -EINVAL;
735
627371d7 736 WARN_ON(!atomic_read(&pi_state->refcount));
59647b6a
TG
737
738 /*
739 * When pi_state->owner is NULL then the owner died
740 * and another waiter is on the fly. pi_state->owner
741 * is fixed up by the task which acquires
742 * pi_state->rt_mutex.
743 *
744 * We do not check for pid == 0 which can happen when
745 * the owner died and robust_list_exit() cleared the
746 * TID.
747 */
748 if (pid && pi_state->owner) {
749 /*
750 * Bail out if user space manipulated the
751 * futex value.
752 */
753 if (pid != task_pid_vnr(pi_state->owner))
754 return -EINVAL;
755 }
627371d7 756
c87e2837 757 atomic_inc(&pi_state->refcount);
d0aa7a70 758 *ps = pi_state;
c87e2837
IM
759
760 return 0;
761 }
762 }
763
764 /*
e3f2ddea 765 * We are the first waiter - try to look up the real owner and attach
778e9a9c 766 * the new pi_state to it, but bail out when TID = 0
c87e2837 767 */
778e9a9c 768 if (!pid)
e3f2ddea 769 return -ESRCH;
c87e2837 770 p = futex_find_get_task(pid);
7a0ea09a
MH
771 if (!p)
772 return -ESRCH;
778e9a9c
AK
773
774 /*
775 * We need to look at the task state flags to figure out,
776 * whether the task is exiting. To protect against the do_exit
777 * change of the task flags, we do this protected by
778 * p->pi_lock:
779 */
1d615482 780 raw_spin_lock_irq(&p->pi_lock);
778e9a9c
AK
781 if (unlikely(p->flags & PF_EXITING)) {
782 /*
783 * The task is on the way out. When PF_EXITPIDONE is
784 * set, we know that the task has finished the
785 * cleanup:
786 */
787 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
788
1d615482 789 raw_spin_unlock_irq(&p->pi_lock);
778e9a9c
AK
790 put_task_struct(p);
791 return ret;
792 }
c87e2837
IM
793
794 pi_state = alloc_pi_state();
795
796 /*
797 * Initialize the pi_mutex in locked state and make 'p'
798 * the owner of it:
799 */
800 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
801
802 /* Store the key for possible exit cleanups: */
d0aa7a70 803 pi_state->key = *key;
c87e2837 804
627371d7 805 WARN_ON(!list_empty(&pi_state->list));
c87e2837
IM
806 list_add(&pi_state->list, &p->pi_state_list);
807 pi_state->owner = p;
1d615482 808 raw_spin_unlock_irq(&p->pi_lock);
c87e2837
IM
809
810 put_task_struct(p);
811
d0aa7a70 812 *ps = pi_state;
c87e2837
IM
813
814 return 0;
815}
816
1a52084d 817/**
d96ee56c 818 * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
bab5bc9e
DH
819 * @uaddr: the pi futex user address
820 * @hb: the pi futex hash bucket
821 * @key: the futex key associated with uaddr and hb
822 * @ps: the pi_state pointer where we store the result of the
823 * lookup
824 * @task: the task to perform the atomic lock work for. This will
825 * be "current" except in the case of requeue pi.
826 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1a52084d 827 *
6c23cbbd
RD
828 * Return:
829 * 0 - ready to wait;
830 * 1 - acquired the lock;
1a52084d
DH
831 * <0 - error
832 *
833 * The hb->lock and futex_key refs shall be held by the caller.
834 */
835static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
836 union futex_key *key,
837 struct futex_pi_state **ps,
bab5bc9e 838 struct task_struct *task, int set_waiters)
1a52084d 839{
59fa6245 840 int lock_taken, ret, force_take = 0;
c0c9ed15 841 u32 uval, newval, curval, vpid = task_pid_vnr(task);
1a52084d
DH
842
843retry:
844 ret = lock_taken = 0;
845
846 /*
847 * To avoid races, we attempt to take the lock here again
848 * (by doing a 0 -> TID atomic cmpxchg), while holding all
849 * the locks. It will most likely not succeed.
850 */
c0c9ed15 851 newval = vpid;
bab5bc9e
DH
852 if (set_waiters)
853 newval |= FUTEX_WAITERS;
1a52084d 854
37a9d912 855 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval)))
1a52084d
DH
856 return -EFAULT;
857
858 /*
859 * Detect deadlocks.
860 */
c0c9ed15 861 if ((unlikely((curval & FUTEX_TID_MASK) == vpid)))
1a52084d
DH
862 return -EDEADLK;
863
864 /*
865 * Surprise - we got the lock. Just return to userspace:
866 */
867 if (unlikely(!curval))
868 return 1;
869
870 uval = curval;
871
872 /*
873 * Set the FUTEX_WAITERS flag, so the owner will know it has someone
874 * to wake at the next unlock.
875 */
876 newval = curval | FUTEX_WAITERS;
877
878 /*
59fa6245 879 * Should we force take the futex? See below.
1a52084d 880 */
59fa6245
TG
881 if (unlikely(force_take)) {
882 /*
883 * Keep the OWNER_DIED and the WAITERS bit and set the
884 * new TID value.
885 */
c0c9ed15 886 newval = (curval & ~FUTEX_TID_MASK) | vpid;
59fa6245 887 force_take = 0;
1a52084d
DH
888 lock_taken = 1;
889 }
890
37a9d912 891 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
1a52084d
DH
892 return -EFAULT;
893 if (unlikely(curval != uval))
894 goto retry;
895
896 /*
59fa6245 897 * We took the lock due to forced take over.
1a52084d
DH
898 */
899 if (unlikely(lock_taken))
900 return 1;
901
902 /*
903 * We dont have the lock. Look up the PI state (or create it if
904 * we are the first waiter):
905 */
906 ret = lookup_pi_state(uval, hb, key, ps);
907
908 if (unlikely(ret)) {
909 switch (ret) {
910 case -ESRCH:
911 /*
59fa6245
TG
912 * We failed to find an owner for this
913 * futex. So we have no pi_state to block
914 * on. This can happen in two cases:
915 *
916 * 1) The owner died
917 * 2) A stale FUTEX_WAITERS bit
918 *
919 * Re-read the futex value.
1a52084d
DH
920 */
921 if (get_futex_value_locked(&curval, uaddr))
922 return -EFAULT;
923
924 /*
59fa6245
TG
925 * If the owner died or we have a stale
926 * WAITERS bit the owner TID in the user space
927 * futex is 0.
1a52084d 928 */
59fa6245
TG
929 if (!(curval & FUTEX_TID_MASK)) {
930 force_take = 1;
1a52084d
DH
931 goto retry;
932 }
933 default:
934 break;
935 }
936 }
937
938 return ret;
939}
940
2e12978a
LJ
941/**
942 * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
943 * @q: The futex_q to unqueue
944 *
945 * The q->lock_ptr must not be NULL and must be held by the caller.
946 */
947static void __unqueue_futex(struct futex_q *q)
948{
949 struct futex_hash_bucket *hb;
950
29096202
SR
951 if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
952 || WARN_ON(plist_node_empty(&q->list)))
2e12978a
LJ
953 return;
954
955 hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
956 plist_del(&q->list, &hb->chain);
957}
958
1da177e4
LT
959/*
960 * The hash bucket lock must be held when this is called.
961 * Afterwards, the futex_q must not be accessed.
962 */
963static void wake_futex(struct futex_q *q)
964{
f1a11e05
TG
965 struct task_struct *p = q->task;
966
aa10990e
DH
967 if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
968 return;
969
1da177e4 970 /*
f1a11e05 971 * We set q->lock_ptr = NULL _before_ we wake up the task. If
fb62db2b
RD
972 * a non-futex wake up happens on another CPU then the task
973 * might exit and p would dereference a non-existing task
f1a11e05
TG
974 * struct. Prevent this by holding a reference on p across the
975 * wake up.
1da177e4 976 */
f1a11e05
TG
977 get_task_struct(p);
978
2e12978a 979 __unqueue_futex(q);
1da177e4 980 /*
f1a11e05
TG
981 * The waiting task can free the futex_q as soon as
982 * q->lock_ptr = NULL is written, without taking any locks. A
983 * memory barrier is required here to prevent the following
984 * store to lock_ptr from getting ahead of the plist_del.
1da177e4 985 */
ccdea2f8 986 smp_wmb();
1da177e4 987 q->lock_ptr = NULL;
f1a11e05
TG
988
989 wake_up_state(p, TASK_NORMAL);
990 put_task_struct(p);
1da177e4
LT
991}
992
c87e2837
IM
993static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
994{
995 struct task_struct *new_owner;
996 struct futex_pi_state *pi_state = this->pi_state;
7cfdaf38 997 u32 uninitialized_var(curval), newval;
c87e2837
IM
998
999 if (!pi_state)
1000 return -EINVAL;
1001
51246bfd
TG
1002 /*
1003 * If current does not own the pi_state then the futex is
1004 * inconsistent and user space fiddled with the futex value.
1005 */
1006 if (pi_state->owner != current)
1007 return -EINVAL;
1008
d209d74d 1009 raw_spin_lock(&pi_state->pi_mutex.wait_lock);
c87e2837
IM
1010 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
1011
1012 /*
f123c98e
SR
1013 * It is possible that the next waiter (the one that brought
1014 * this owner to the kernel) timed out and is no longer
1015 * waiting on the lock.
c87e2837
IM
1016 */
1017 if (!new_owner)
1018 new_owner = this->task;
1019
1020 /*
1021 * We pass it to the next owner. (The WAITERS bit is always
1022 * kept enabled while there is PI state around. We must also
1023 * preserve the owner died bit.)
1024 */
e3f2ddea 1025 if (!(uval & FUTEX_OWNER_DIED)) {
778e9a9c
AK
1026 int ret = 0;
1027
b488893a 1028 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
e3f2ddea 1029
37a9d912 1030 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
778e9a9c 1031 ret = -EFAULT;
cde898fa 1032 else if (curval != uval)
778e9a9c
AK
1033 ret = -EINVAL;
1034 if (ret) {
d209d74d 1035 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
778e9a9c
AK
1036 return ret;
1037 }
e3f2ddea 1038 }
c87e2837 1039
1d615482 1040 raw_spin_lock_irq(&pi_state->owner->pi_lock);
627371d7
IM
1041 WARN_ON(list_empty(&pi_state->list));
1042 list_del_init(&pi_state->list);
1d615482 1043 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
627371d7 1044
1d615482 1045 raw_spin_lock_irq(&new_owner->pi_lock);
627371d7 1046 WARN_ON(!list_empty(&pi_state->list));
c87e2837
IM
1047 list_add(&pi_state->list, &new_owner->pi_state_list);
1048 pi_state->owner = new_owner;
1d615482 1049 raw_spin_unlock_irq(&new_owner->pi_lock);
627371d7 1050
d209d74d 1051 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
c87e2837
IM
1052 rt_mutex_unlock(&pi_state->pi_mutex);
1053
1054 return 0;
1055}
1056
1057static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
1058{
7cfdaf38 1059 u32 uninitialized_var(oldval);
c87e2837
IM
1060
1061 /*
1062 * There is no waiter, so we unlock the futex. The owner died
1063 * bit has not to be preserved here. We are the owner:
1064 */
37a9d912
ML
1065 if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0))
1066 return -EFAULT;
c87e2837
IM
1067 if (oldval != uval)
1068 return -EAGAIN;
1069
1070 return 0;
1071}
1072
8b8f319f
IM
1073/*
1074 * Express the locking dependencies for lockdep:
1075 */
1076static inline void
1077double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1078{
1079 if (hb1 <= hb2) {
1080 spin_lock(&hb1->lock);
1081 if (hb1 < hb2)
1082 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
1083 } else { /* hb1 > hb2 */
1084 spin_lock(&hb2->lock);
1085 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
1086 }
1087}
1088
5eb3dc62
DH
1089static inline void
1090double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1091{
f061d351 1092 spin_unlock(&hb1->lock);
88f502fe
IM
1093 if (hb1 != hb2)
1094 spin_unlock(&hb2->lock);
5eb3dc62
DH
1095}
1096
1da177e4 1097/*
b2d0994b 1098 * Wake up waiters matching bitset queued on this futex (uaddr).
1da177e4 1099 */
b41277dc
DH
1100static int
1101futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
1da177e4 1102{
e2970f2f 1103 struct futex_hash_bucket *hb;
1da177e4 1104 struct futex_q *this, *next;
38d47c1b 1105 union futex_key key = FUTEX_KEY_INIT;
1da177e4
LT
1106 int ret;
1107
cd689985
TG
1108 if (!bitset)
1109 return -EINVAL;
1110
9ea71503 1111 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
1da177e4
LT
1112 if (unlikely(ret != 0))
1113 goto out;
1114
e2970f2f 1115 hb = hash_futex(&key);
b0c29f79
DB
1116
1117 /* Make sure we really have tasks to wakeup */
1118 if (!hb_waiters_pending(hb))
1119 goto out_put_key;
1120
e2970f2f 1121 spin_lock(&hb->lock);
1da177e4 1122
0d00c7b2 1123 plist_for_each_entry_safe(this, next, &hb->chain, list) {
1da177e4 1124 if (match_futex (&this->key, &key)) {
52400ba9 1125 if (this->pi_state || this->rt_waiter) {
ed6f7b10
IM
1126 ret = -EINVAL;
1127 break;
1128 }
cd689985
TG
1129
1130 /* Check if one of the bits is set in both bitsets */
1131 if (!(this->bitset & bitset))
1132 continue;
1133
1da177e4
LT
1134 wake_futex(this);
1135 if (++ret >= nr_wake)
1136 break;
1137 }
1138 }
1139
e2970f2f 1140 spin_unlock(&hb->lock);
b0c29f79 1141out_put_key:
ae791a2d 1142 put_futex_key(&key);
42d35d48 1143out:
1da177e4
LT
1144 return ret;
1145}
1146
4732efbe
JJ
1147/*
1148 * Wake up all waiters hashed on the physical page that is mapped
1149 * to this virtual address:
1150 */
e2970f2f 1151static int
b41277dc 1152futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
e2970f2f 1153 int nr_wake, int nr_wake2, int op)
4732efbe 1154{
38d47c1b 1155 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
e2970f2f 1156 struct futex_hash_bucket *hb1, *hb2;
4732efbe 1157 struct futex_q *this, *next;
e4dc5b7a 1158 int ret, op_ret;
4732efbe 1159
e4dc5b7a 1160retry:
9ea71503 1161 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
4732efbe
JJ
1162 if (unlikely(ret != 0))
1163 goto out;
9ea71503 1164 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
4732efbe 1165 if (unlikely(ret != 0))
42d35d48 1166 goto out_put_key1;
4732efbe 1167
e2970f2f
IM
1168 hb1 = hash_futex(&key1);
1169 hb2 = hash_futex(&key2);
4732efbe 1170
e4dc5b7a 1171retry_private:
eaaea803 1172 double_lock_hb(hb1, hb2);
e2970f2f 1173 op_ret = futex_atomic_op_inuser(op, uaddr2);
4732efbe 1174 if (unlikely(op_ret < 0)) {
4732efbe 1175
5eb3dc62 1176 double_unlock_hb(hb1, hb2);
4732efbe 1177
7ee1dd3f 1178#ifndef CONFIG_MMU
e2970f2f
IM
1179 /*
1180 * we don't get EFAULT from MMU faults if we don't have an MMU,
1181 * but we might get them from range checking
1182 */
7ee1dd3f 1183 ret = op_ret;
42d35d48 1184 goto out_put_keys;
7ee1dd3f
DH
1185#endif
1186
796f8d9b
DG
1187 if (unlikely(op_ret != -EFAULT)) {
1188 ret = op_ret;
42d35d48 1189 goto out_put_keys;
796f8d9b
DG
1190 }
1191
d0725992 1192 ret = fault_in_user_writeable(uaddr2);
4732efbe 1193 if (ret)
de87fcc1 1194 goto out_put_keys;
4732efbe 1195
b41277dc 1196 if (!(flags & FLAGS_SHARED))
e4dc5b7a
DH
1197 goto retry_private;
1198
ae791a2d
TG
1199 put_futex_key(&key2);
1200 put_futex_key(&key1);
e4dc5b7a 1201 goto retry;
4732efbe
JJ
1202 }
1203
0d00c7b2 1204 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
4732efbe 1205 if (match_futex (&this->key, &key1)) {
aa10990e
DH
1206 if (this->pi_state || this->rt_waiter) {
1207 ret = -EINVAL;
1208 goto out_unlock;
1209 }
4732efbe
JJ
1210 wake_futex(this);
1211 if (++ret >= nr_wake)
1212 break;
1213 }
1214 }
1215
1216 if (op_ret > 0) {
4732efbe 1217 op_ret = 0;
0d00c7b2 1218 plist_for_each_entry_safe(this, next, &hb2->chain, list) {
4732efbe 1219 if (match_futex (&this->key, &key2)) {
aa10990e
DH
1220 if (this->pi_state || this->rt_waiter) {
1221 ret = -EINVAL;
1222 goto out_unlock;
1223 }
4732efbe
JJ
1224 wake_futex(this);
1225 if (++op_ret >= nr_wake2)
1226 break;
1227 }
1228 }
1229 ret += op_ret;
1230 }
1231
aa10990e 1232out_unlock:
5eb3dc62 1233 double_unlock_hb(hb1, hb2);
42d35d48 1234out_put_keys:
ae791a2d 1235 put_futex_key(&key2);
42d35d48 1236out_put_key1:
ae791a2d 1237 put_futex_key(&key1);
42d35d48 1238out:
4732efbe
JJ
1239 return ret;
1240}
1241
9121e478
DH
1242/**
1243 * requeue_futex() - Requeue a futex_q from one hb to another
1244 * @q: the futex_q to requeue
1245 * @hb1: the source hash_bucket
1246 * @hb2: the target hash_bucket
1247 * @key2: the new key for the requeued futex_q
1248 */
1249static inline
1250void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1251 struct futex_hash_bucket *hb2, union futex_key *key2)
1252{
1253
1254 /*
1255 * If key1 and key2 hash to the same bucket, no need to
1256 * requeue.
1257 */
1258 if (likely(&hb1->chain != &hb2->chain)) {
1259 plist_del(&q->list, &hb1->chain);
1260 plist_add(&q->list, &hb2->chain);
1261 q->lock_ptr = &hb2->lock;
9121e478
DH
1262 }
1263 get_futex_key_refs(key2);
1264 q->key = *key2;
1265}
1266
52400ba9
DH
1267/**
1268 * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
d96ee56c
DH
1269 * @q: the futex_q
1270 * @key: the key of the requeue target futex
1271 * @hb: the hash_bucket of the requeue target futex
52400ba9
DH
1272 *
1273 * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1274 * target futex if it is uncontended or via a lock steal. Set the futex_q key
1275 * to the requeue target futex so the waiter can detect the wakeup on the right
1276 * futex, but remove it from the hb and NULL the rt_waiter so it can detect
beda2c7e
DH
1277 * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
1278 * to protect access to the pi_state to fixup the owner later. Must be called
1279 * with both q->lock_ptr and hb->lock held.
52400ba9
DH
1280 */
1281static inline
beda2c7e
DH
1282void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1283 struct futex_hash_bucket *hb)
52400ba9 1284{
52400ba9
DH
1285 get_futex_key_refs(key);
1286 q->key = *key;
1287
2e12978a 1288 __unqueue_futex(q);
52400ba9
DH
1289
1290 WARN_ON(!q->rt_waiter);
1291 q->rt_waiter = NULL;
1292
beda2c7e 1293 q->lock_ptr = &hb->lock;
beda2c7e 1294
f1a11e05 1295 wake_up_state(q->task, TASK_NORMAL);
52400ba9
DH
1296}
1297
1298/**
1299 * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
bab5bc9e
DH
1300 * @pifutex: the user address of the to futex
1301 * @hb1: the from futex hash bucket, must be locked by the caller
1302 * @hb2: the to futex hash bucket, must be locked by the caller
1303 * @key1: the from futex key
1304 * @key2: the to futex key
1305 * @ps: address to store the pi_state pointer
1306 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
52400ba9
DH
1307 *
1308 * Try and get the lock on behalf of the top waiter if we can do it atomically.
bab5bc9e
DH
1309 * Wake the top waiter if we succeed. If the caller specified set_waiters,
1310 * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1311 * hb1 and hb2 must be held by the caller.
52400ba9 1312 *
6c23cbbd
RD
1313 * Return:
1314 * 0 - failed to acquire the lock atomically;
1315 * 1 - acquired the lock;
52400ba9
DH
1316 * <0 - error
1317 */
1318static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1319 struct futex_hash_bucket *hb1,
1320 struct futex_hash_bucket *hb2,
1321 union futex_key *key1, union futex_key *key2,
bab5bc9e 1322 struct futex_pi_state **ps, int set_waiters)
52400ba9 1323{
bab5bc9e 1324 struct futex_q *top_waiter = NULL;
52400ba9
DH
1325 u32 curval;
1326 int ret;
1327
1328 if (get_futex_value_locked(&curval, pifutex))
1329 return -EFAULT;
1330
bab5bc9e
DH
1331 /*
1332 * Find the top_waiter and determine if there are additional waiters.
1333 * If the caller intends to requeue more than 1 waiter to pifutex,
1334 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1335 * as we have means to handle the possible fault. If not, don't set
1336 * the bit unecessarily as it will force the subsequent unlock to enter
1337 * the kernel.
1338 */
52400ba9
DH
1339 top_waiter = futex_top_waiter(hb1, key1);
1340
1341 /* There are no waiters, nothing for us to do. */
1342 if (!top_waiter)
1343 return 0;
1344
84bc4af5
DH
1345 /* Ensure we requeue to the expected futex. */
1346 if (!match_futex(top_waiter->requeue_pi_key, key2))
1347 return -EINVAL;
1348
52400ba9 1349 /*
bab5bc9e
DH
1350 * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
1351 * the contended case or if set_waiters is 1. The pi_state is returned
1352 * in ps in contended cases.
52400ba9 1353 */
bab5bc9e
DH
1354 ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1355 set_waiters);
52400ba9 1356 if (ret == 1)
beda2c7e 1357 requeue_pi_wake_futex(top_waiter, key2, hb2);
52400ba9
DH
1358
1359 return ret;
1360}
1361
1362/**
1363 * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
fb62db2b 1364 * @uaddr1: source futex user address
b41277dc 1365 * @flags: futex flags (FLAGS_SHARED, etc.)
fb62db2b
RD
1366 * @uaddr2: target futex user address
1367 * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
1368 * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1369 * @cmpval: @uaddr1 expected value (or %NULL)
1370 * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
b41277dc 1371 * pi futex (pi to pi requeue is not supported)
52400ba9
DH
1372 *
1373 * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1374 * uaddr2 atomically on behalf of the top waiter.
1375 *
6c23cbbd
RD
1376 * Return:
1377 * >=0 - on success, the number of tasks requeued or woken;
52400ba9 1378 * <0 - on error
1da177e4 1379 */
b41277dc
DH
1380static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1381 u32 __user *uaddr2, int nr_wake, int nr_requeue,
1382 u32 *cmpval, int requeue_pi)
1da177e4 1383{
38d47c1b 1384 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
52400ba9
DH
1385 int drop_count = 0, task_count = 0, ret;
1386 struct futex_pi_state *pi_state = NULL;
e2970f2f 1387 struct futex_hash_bucket *hb1, *hb2;
1da177e4 1388 struct futex_q *this, *next;
52400ba9
DH
1389 u32 curval2;
1390
1391 if (requeue_pi) {
1392 /*
1393 * requeue_pi requires a pi_state, try to allocate it now
1394 * without any locks in case it fails.
1395 */
1396 if (refill_pi_state_cache())
1397 return -ENOMEM;
1398 /*
1399 * requeue_pi must wake as many tasks as it can, up to nr_wake
1400 * + nr_requeue, since it acquires the rt_mutex prior to
1401 * returning to userspace, so as to not leave the rt_mutex with
1402 * waiters and no owner. However, second and third wake-ups
1403 * cannot be predicted as they involve race conditions with the
1404 * first wake and a fault while looking up the pi_state. Both
1405 * pthread_cond_signal() and pthread_cond_broadcast() should
1406 * use nr_wake=1.
1407 */
1408 if (nr_wake != 1)
1409 return -EINVAL;
1410 }
1da177e4 1411
42d35d48 1412retry:
52400ba9
DH
1413 if (pi_state != NULL) {
1414 /*
1415 * We will have to lookup the pi_state again, so free this one
1416 * to keep the accounting correct.
1417 */
1418 free_pi_state(pi_state);
1419 pi_state = NULL;
1420 }
1421
9ea71503 1422 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1da177e4
LT
1423 if (unlikely(ret != 0))
1424 goto out;
9ea71503
SB
1425 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
1426 requeue_pi ? VERIFY_WRITE : VERIFY_READ);
1da177e4 1427 if (unlikely(ret != 0))
42d35d48 1428 goto out_put_key1;
1da177e4 1429
e2970f2f
IM
1430 hb1 = hash_futex(&key1);
1431 hb2 = hash_futex(&key2);
1da177e4 1432
e4dc5b7a 1433retry_private:
8b8f319f 1434 double_lock_hb(hb1, hb2);
1da177e4 1435
e2970f2f
IM
1436 if (likely(cmpval != NULL)) {
1437 u32 curval;
1da177e4 1438
e2970f2f 1439 ret = get_futex_value_locked(&curval, uaddr1);
1da177e4
LT
1440
1441 if (unlikely(ret)) {
5eb3dc62 1442 double_unlock_hb(hb1, hb2);
1da177e4 1443
e2970f2f 1444 ret = get_user(curval, uaddr1);
e4dc5b7a
DH
1445 if (ret)
1446 goto out_put_keys;
1da177e4 1447
b41277dc 1448 if (!(flags & FLAGS_SHARED))
e4dc5b7a 1449 goto retry_private;
1da177e4 1450
ae791a2d
TG
1451 put_futex_key(&key2);
1452 put_futex_key(&key1);
e4dc5b7a 1453 goto retry;
1da177e4 1454 }
e2970f2f 1455 if (curval != *cmpval) {
1da177e4
LT
1456 ret = -EAGAIN;
1457 goto out_unlock;
1458 }
1459 }
1460
52400ba9 1461 if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
bab5bc9e
DH
1462 /*
1463 * Attempt to acquire uaddr2 and wake the top waiter. If we
1464 * intend to requeue waiters, force setting the FUTEX_WAITERS
1465 * bit. We force this here where we are able to easily handle
1466 * faults rather in the requeue loop below.
1467 */
52400ba9 1468 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
bab5bc9e 1469 &key2, &pi_state, nr_requeue);
52400ba9
DH
1470
1471 /*
1472 * At this point the top_waiter has either taken uaddr2 or is
1473 * waiting on it. If the former, then the pi_state will not
1474 * exist yet, look it up one more time to ensure we have a
1475 * reference to it.
1476 */
1477 if (ret == 1) {
1478 WARN_ON(pi_state);
89061d3d 1479 drop_count++;
52400ba9
DH
1480 task_count++;
1481 ret = get_futex_value_locked(&curval2, uaddr2);
1482 if (!ret)
1483 ret = lookup_pi_state(curval2, hb2, &key2,
1484 &pi_state);
1485 }
1486
1487 switch (ret) {
1488 case 0:
1489 break;
1490 case -EFAULT:
1491 double_unlock_hb(hb1, hb2);
ae791a2d
TG
1492 put_futex_key(&key2);
1493 put_futex_key(&key1);
d0725992 1494 ret = fault_in_user_writeable(uaddr2);
52400ba9
DH
1495 if (!ret)
1496 goto retry;
1497 goto out;
1498 case -EAGAIN:
1499 /* The owner was exiting, try again. */
1500 double_unlock_hb(hb1, hb2);
ae791a2d
TG
1501 put_futex_key(&key2);
1502 put_futex_key(&key1);
52400ba9
DH
1503 cond_resched();
1504 goto retry;
1505 default:
1506 goto out_unlock;
1507 }
1508 }
1509
0d00c7b2 1510 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
52400ba9
DH
1511 if (task_count - nr_wake >= nr_requeue)
1512 break;
1513
1514 if (!match_futex(&this->key, &key1))
1da177e4 1515 continue;
52400ba9 1516
392741e0
DH
1517 /*
1518 * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1519 * be paired with each other and no other futex ops.
aa10990e
DH
1520 *
1521 * We should never be requeueing a futex_q with a pi_state,
1522 * which is awaiting a futex_unlock_pi().
392741e0
DH
1523 */
1524 if ((requeue_pi && !this->rt_waiter) ||
aa10990e
DH
1525 (!requeue_pi && this->rt_waiter) ||
1526 this->pi_state) {
392741e0
DH
1527 ret = -EINVAL;
1528 break;
1529 }
52400ba9
DH
1530
1531 /*
1532 * Wake nr_wake waiters. For requeue_pi, if we acquired the
1533 * lock, we already woke the top_waiter. If not, it will be
1534 * woken by futex_unlock_pi().
1535 */
1536 if (++task_count <= nr_wake && !requeue_pi) {
1da177e4 1537 wake_futex(this);
52400ba9
DH
1538 continue;
1539 }
1da177e4 1540
84bc4af5
DH
1541 /* Ensure we requeue to the expected futex for requeue_pi. */
1542 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1543 ret = -EINVAL;
1544 break;
1545 }
1546
52400ba9
DH
1547 /*
1548 * Requeue nr_requeue waiters and possibly one more in the case
1549 * of requeue_pi if we couldn't acquire the lock atomically.
1550 */
1551 if (requeue_pi) {
1552 /* Prepare the waiter to take the rt_mutex. */
1553 atomic_inc(&pi_state->refcount);
1554 this->pi_state = pi_state;
1555 ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1556 this->rt_waiter,
1557 this->task, 1);
1558 if (ret == 1) {
1559 /* We got the lock. */
beda2c7e 1560 requeue_pi_wake_futex(this, &key2, hb2);
89061d3d 1561 drop_count++;
52400ba9
DH
1562 continue;
1563 } else if (ret) {
1564 /* -EDEADLK */
1565 this->pi_state = NULL;
1566 free_pi_state(pi_state);
1567 goto out_unlock;
1568 }
1da177e4 1569 }
52400ba9
DH
1570 requeue_futex(this, hb1, hb2, &key2);
1571 drop_count++;
1da177e4
LT
1572 }
1573
1574out_unlock:
5eb3dc62 1575 double_unlock_hb(hb1, hb2);
1da177e4 1576
cd84a42f
DH
1577 /*
1578 * drop_futex_key_refs() must be called outside the spinlocks. During
1579 * the requeue we moved futex_q's from the hash bucket at key1 to the
1580 * one at key2 and updated their key pointer. We no longer need to
1581 * hold the references to key1.
1582 */
1da177e4 1583 while (--drop_count >= 0)
9adef58b 1584 drop_futex_key_refs(&key1);
1da177e4 1585
42d35d48 1586out_put_keys:
ae791a2d 1587 put_futex_key(&key2);
42d35d48 1588out_put_key1:
ae791a2d 1589 put_futex_key(&key1);
42d35d48 1590out:
52400ba9
DH
1591 if (pi_state != NULL)
1592 free_pi_state(pi_state);
1593 return ret ? ret : task_count;
1da177e4
LT
1594}
1595
1596/* The key must be already stored in q->key. */
82af7aca 1597static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
15e408cd 1598 __acquires(&hb->lock)
1da177e4 1599{
e2970f2f 1600 struct futex_hash_bucket *hb;
1da177e4 1601
e2970f2f
IM
1602 hb = hash_futex(&q->key);
1603 q->lock_ptr = &hb->lock;
1da177e4 1604
b0c29f79 1605 spin_lock(&hb->lock); /* implies MB (A) */
e2970f2f 1606 return hb;
1da177e4
LT
1607}
1608
d40d65c8 1609static inline void
0d00c7b2 1610queue_unlock(struct futex_hash_bucket *hb)
15e408cd 1611 __releases(&hb->lock)
d40d65c8
DH
1612{
1613 spin_unlock(&hb->lock);
d40d65c8
DH
1614}
1615
1616/**
1617 * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1618 * @q: The futex_q to enqueue
1619 * @hb: The destination hash bucket
1620 *
1621 * The hb->lock must be held by the caller, and is released here. A call to
1622 * queue_me() is typically paired with exactly one call to unqueue_me(). The
1623 * exceptions involve the PI related operations, which may use unqueue_me_pi()
1624 * or nothing if the unqueue is done as part of the wake process and the unqueue
1625 * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1626 * an example).
1627 */
82af7aca 1628static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
15e408cd 1629 __releases(&hb->lock)
1da177e4 1630{
ec92d082
PP
1631 int prio;
1632
1633 /*
1634 * The priority used to register this element is
1635 * - either the real thread-priority for the real-time threads
1636 * (i.e. threads with a priority lower than MAX_RT_PRIO)
1637 * - or MAX_RT_PRIO for non-RT threads.
1638 * Thus, all RT-threads are woken first in priority order, and
1639 * the others are woken last, in FIFO order.
1640 */
1641 prio = min(current->normal_prio, MAX_RT_PRIO);
1642
1643 plist_node_init(&q->list, prio);
ec92d082 1644 plist_add(&q->list, &hb->chain);
c87e2837 1645 q->task = current;
e2970f2f 1646 spin_unlock(&hb->lock);
1da177e4
LT
1647}
1648
d40d65c8
DH
1649/**
1650 * unqueue_me() - Remove the futex_q from its futex_hash_bucket
1651 * @q: The futex_q to unqueue
1652 *
1653 * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
1654 * be paired with exactly one earlier call to queue_me().
1655 *
6c23cbbd
RD
1656 * Return:
1657 * 1 - if the futex_q was still queued (and we removed unqueued it);
d40d65c8 1658 * 0 - if the futex_q was already removed by the waking thread
1da177e4 1659 */
1da177e4
LT
1660static int unqueue_me(struct futex_q *q)
1661{
1da177e4 1662 spinlock_t *lock_ptr;
e2970f2f 1663 int ret = 0;
1da177e4
LT
1664
1665 /* In the common case we don't take the spinlock, which is nice. */
42d35d48 1666retry:
1da177e4 1667 lock_ptr = q->lock_ptr;
e91467ec 1668 barrier();
c80544dc 1669 if (lock_ptr != NULL) {
1da177e4
LT
1670 spin_lock(lock_ptr);
1671 /*
1672 * q->lock_ptr can change between reading it and
1673 * spin_lock(), causing us to take the wrong lock. This
1674 * corrects the race condition.
1675 *
1676 * Reasoning goes like this: if we have the wrong lock,
1677 * q->lock_ptr must have changed (maybe several times)
1678 * between reading it and the spin_lock(). It can
1679 * change again after the spin_lock() but only if it was
1680 * already changed before the spin_lock(). It cannot,
1681 * however, change back to the original value. Therefore
1682 * we can detect whether we acquired the correct lock.
1683 */
1684 if (unlikely(lock_ptr != q->lock_ptr)) {
1685 spin_unlock(lock_ptr);
1686 goto retry;
1687 }
2e12978a 1688 __unqueue_futex(q);
c87e2837
IM
1689
1690 BUG_ON(q->pi_state);
1691
1da177e4
LT
1692 spin_unlock(lock_ptr);
1693 ret = 1;
1694 }
1695
9adef58b 1696 drop_futex_key_refs(&q->key);
1da177e4
LT
1697 return ret;
1698}
1699
c87e2837
IM
1700/*
1701 * PI futexes can not be requeued and must remove themself from the
d0aa7a70
PP
1702 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1703 * and dropped here.
c87e2837 1704 */
d0aa7a70 1705static void unqueue_me_pi(struct futex_q *q)
15e408cd 1706 __releases(q->lock_ptr)
c87e2837 1707{
2e12978a 1708 __unqueue_futex(q);
c87e2837
IM
1709
1710 BUG_ON(!q->pi_state);
1711 free_pi_state(q->pi_state);
1712 q->pi_state = NULL;
1713
d0aa7a70 1714 spin_unlock(q->lock_ptr);
c87e2837
IM
1715}
1716
d0aa7a70 1717/*
cdf71a10 1718 * Fixup the pi_state owner with the new owner.
d0aa7a70 1719 *
778e9a9c
AK
1720 * Must be called with hash bucket lock held and mm->sem held for non
1721 * private futexes.
d0aa7a70 1722 */
778e9a9c 1723static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
ae791a2d 1724 struct task_struct *newowner)
d0aa7a70 1725{
cdf71a10 1726 u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
d0aa7a70 1727 struct futex_pi_state *pi_state = q->pi_state;
1b7558e4 1728 struct task_struct *oldowner = pi_state->owner;
7cfdaf38 1729 u32 uval, uninitialized_var(curval), newval;
e4dc5b7a 1730 int ret;
d0aa7a70
PP
1731
1732 /* Owner died? */
1b7558e4
TG
1733 if (!pi_state->owner)
1734 newtid |= FUTEX_OWNER_DIED;
1735
1736 /*
1737 * We are here either because we stole the rtmutex from the
8161239a
LJ
1738 * previous highest priority waiter or we are the highest priority
1739 * waiter but failed to get the rtmutex the first time.
1740 * We have to replace the newowner TID in the user space variable.
1741 * This must be atomic as we have to preserve the owner died bit here.
1b7558e4 1742 *
b2d0994b
DH
1743 * Note: We write the user space value _before_ changing the pi_state
1744 * because we can fault here. Imagine swapped out pages or a fork
1745 * that marked all the anonymous memory readonly for cow.
1b7558e4
TG
1746 *
1747 * Modifying pi_state _before_ the user space value would
1748 * leave the pi_state in an inconsistent state when we fault
1749 * here, because we need to drop the hash bucket lock to
1750 * handle the fault. This might be observed in the PID check
1751 * in lookup_pi_state.
1752 */
1753retry:
1754 if (get_futex_value_locked(&uval, uaddr))
1755 goto handle_fault;
1756
1757 while (1) {
1758 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1759
37a9d912 1760 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
1b7558e4
TG
1761 goto handle_fault;
1762 if (curval == uval)
1763 break;
1764 uval = curval;
1765 }
1766
1767 /*
1768 * We fixed up user space. Now we need to fix the pi_state
1769 * itself.
1770 */
d0aa7a70 1771 if (pi_state->owner != NULL) {
1d615482 1772 raw_spin_lock_irq(&pi_state->owner->pi_lock);
d0aa7a70
PP
1773 WARN_ON(list_empty(&pi_state->list));
1774 list_del_init(&pi_state->list);
1d615482 1775 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1b7558e4 1776 }
d0aa7a70 1777
cdf71a10 1778 pi_state->owner = newowner;
d0aa7a70 1779
1d615482 1780 raw_spin_lock_irq(&newowner->pi_lock);
d0aa7a70 1781 WARN_ON(!list_empty(&pi_state->list));
cdf71a10 1782 list_add(&pi_state->list, &newowner->pi_state_list);
1d615482 1783 raw_spin_unlock_irq(&newowner->pi_lock);
1b7558e4 1784 return 0;
d0aa7a70 1785
d0aa7a70 1786 /*
1b7558e4 1787 * To handle the page fault we need to drop the hash bucket
8161239a
LJ
1788 * lock here. That gives the other task (either the highest priority
1789 * waiter itself or the task which stole the rtmutex) the
1b7558e4
TG
1790 * chance to try the fixup of the pi_state. So once we are
1791 * back from handling the fault we need to check the pi_state
1792 * after reacquiring the hash bucket lock and before trying to
1793 * do another fixup. When the fixup has been done already we
1794 * simply return.
d0aa7a70 1795 */
1b7558e4
TG
1796handle_fault:
1797 spin_unlock(q->lock_ptr);
778e9a9c 1798
d0725992 1799 ret = fault_in_user_writeable(uaddr);
778e9a9c 1800
1b7558e4 1801 spin_lock(q->lock_ptr);
778e9a9c 1802
1b7558e4
TG
1803 /*
1804 * Check if someone else fixed it for us:
1805 */
1806 if (pi_state->owner != oldowner)
1807 return 0;
1808
1809 if (ret)
1810 return ret;
1811
1812 goto retry;
d0aa7a70
PP
1813}
1814
72c1bbf3 1815static long futex_wait_restart(struct restart_block *restart);
36cf3b5c 1816
dd973998
DH
1817/**
1818 * fixup_owner() - Post lock pi_state and corner case management
1819 * @uaddr: user address of the futex
dd973998
DH
1820 * @q: futex_q (contains pi_state and access to the rt_mutex)
1821 * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
1822 *
1823 * After attempting to lock an rt_mutex, this function is called to cleanup
1824 * the pi_state owner as well as handle race conditions that may allow us to
1825 * acquire the lock. Must be called with the hb lock held.
1826 *
6c23cbbd
RD
1827 * Return:
1828 * 1 - success, lock taken;
1829 * 0 - success, lock not taken;
dd973998
DH
1830 * <0 - on error (-EFAULT)
1831 */
ae791a2d 1832static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
dd973998
DH
1833{
1834 struct task_struct *owner;
1835 int ret = 0;
1836
1837 if (locked) {
1838 /*
1839 * Got the lock. We might not be the anticipated owner if we
1840 * did a lock-steal - fix up the PI-state in that case:
1841 */
1842 if (q->pi_state->owner != current)
ae791a2d 1843 ret = fixup_pi_state_owner(uaddr, q, current);
dd973998
DH
1844 goto out;
1845 }
1846
1847 /*
1848 * Catch the rare case, where the lock was released when we were on the
1849 * way back before we locked the hash bucket.
1850 */
1851 if (q->pi_state->owner == current) {
1852 /*
1853 * Try to get the rt_mutex now. This might fail as some other
1854 * task acquired the rt_mutex after we removed ourself from the
1855 * rt_mutex waiters list.
1856 */
1857 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
1858 locked = 1;
1859 goto out;
1860 }
1861
1862 /*
1863 * pi_state is incorrect, some other task did a lock steal and
1864 * we returned due to timeout or signal without taking the
8161239a 1865 * rt_mutex. Too late.
dd973998 1866 */
8161239a 1867 raw_spin_lock(&q->pi_state->pi_mutex.wait_lock);
dd973998 1868 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
8161239a
LJ
1869 if (!owner)
1870 owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
1871 raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock);
ae791a2d 1872 ret = fixup_pi_state_owner(uaddr, q, owner);
dd973998
DH
1873 goto out;
1874 }
1875
1876 /*
1877 * Paranoia check. If we did not take the lock, then we should not be
8161239a 1878 * the owner of the rt_mutex.
dd973998
DH
1879 */
1880 if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
1881 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
1882 "pi-state %p\n", ret,
1883 q->pi_state->pi_mutex.owner,
1884 q->pi_state->owner);
1885
1886out:
1887 return ret ? ret : locked;
1888}
1889
ca5f9524
DH
1890/**
1891 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
1892 * @hb: the futex hash bucket, must be locked by the caller
1893 * @q: the futex_q to queue up on
1894 * @timeout: the prepared hrtimer_sleeper, or null for no timeout
ca5f9524
DH
1895 */
1896static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
f1a11e05 1897 struct hrtimer_sleeper *timeout)
ca5f9524 1898{
9beba3c5
DH
1899 /*
1900 * The task state is guaranteed to be set before another task can
1901 * wake it. set_current_state() is implemented using set_mb() and
1902 * queue_me() calls spin_unlock() upon completion, both serializing
1903 * access to the hash list and forcing another memory barrier.
1904 */
f1a11e05 1905 set_current_state(TASK_INTERRUPTIBLE);
0729e196 1906 queue_me(q, hb);
ca5f9524
DH
1907
1908 /* Arm the timer */
1909 if (timeout) {
1910 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1911 if (!hrtimer_active(&timeout->timer))
1912 timeout->task = NULL;
1913 }
1914
1915 /*
0729e196
DH
1916 * If we have been removed from the hash list, then another task
1917 * has tried to wake us, and we can skip the call to schedule().
ca5f9524
DH
1918 */
1919 if (likely(!plist_node_empty(&q->list))) {
1920 /*
1921 * If the timer has already expired, current will already be
1922 * flagged for rescheduling. Only call schedule if there
1923 * is no timeout, or if it has yet to expire.
1924 */
1925 if (!timeout || timeout->task)
88c8004f 1926 freezable_schedule();
ca5f9524
DH
1927 }
1928 __set_current_state(TASK_RUNNING);
1929}
1930
f801073f
DH
1931/**
1932 * futex_wait_setup() - Prepare to wait on a futex
1933 * @uaddr: the futex userspace address
1934 * @val: the expected value
b41277dc 1935 * @flags: futex flags (FLAGS_SHARED, etc.)
f801073f
DH
1936 * @q: the associated futex_q
1937 * @hb: storage for hash_bucket pointer to be returned to caller
1938 *
1939 * Setup the futex_q and locate the hash_bucket. Get the futex value and
1940 * compare it with the expected value. Handle atomic faults internally.
1941 * Return with the hb lock held and a q.key reference on success, and unlocked
1942 * with no q.key reference on failure.
1943 *
6c23cbbd
RD
1944 * Return:
1945 * 0 - uaddr contains val and hb has been locked;
ca4a04cf 1946 * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
f801073f 1947 */
b41277dc 1948static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
f801073f 1949 struct futex_q *q, struct futex_hash_bucket **hb)
1da177e4 1950{
e2970f2f
IM
1951 u32 uval;
1952 int ret;
1da177e4 1953
1da177e4 1954 /*
b2d0994b 1955 * Access the page AFTER the hash-bucket is locked.
1da177e4
LT
1956 * Order is important:
1957 *
1958 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1959 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
1960 *
1961 * The basic logical guarantee of a futex is that it blocks ONLY
1962 * if cond(var) is known to be true at the time of blocking, for
8fe8f545
ML
1963 * any cond. If we locked the hash-bucket after testing *uaddr, that
1964 * would open a race condition where we could block indefinitely with
1da177e4
LT
1965 * cond(var) false, which would violate the guarantee.
1966 *
8fe8f545
ML
1967 * On the other hand, we insert q and release the hash-bucket only
1968 * after testing *uaddr. This guarantees that futex_wait() will NOT
1969 * absorb a wakeup if *uaddr does not match the desired values
1970 * while the syscall executes.
1da177e4 1971 */
f801073f 1972retry:
9ea71503 1973 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
f801073f 1974 if (unlikely(ret != 0))
a5a2a0c7 1975 return ret;
f801073f
DH
1976
1977retry_private:
1978 *hb = queue_lock(q);
1979
e2970f2f 1980 ret = get_futex_value_locked(&uval, uaddr);
1da177e4 1981
f801073f 1982 if (ret) {
0d00c7b2 1983 queue_unlock(*hb);
1da177e4 1984
e2970f2f 1985 ret = get_user(uval, uaddr);
e4dc5b7a 1986 if (ret)
f801073f 1987 goto out;
1da177e4 1988
b41277dc 1989 if (!(flags & FLAGS_SHARED))
e4dc5b7a
DH
1990 goto retry_private;
1991
ae791a2d 1992 put_futex_key(&q->key);
e4dc5b7a 1993 goto retry;
1da177e4 1994 }
ca5f9524 1995
f801073f 1996 if (uval != val) {
0d00c7b2 1997 queue_unlock(*hb);
f801073f 1998 ret = -EWOULDBLOCK;
2fff78c7 1999 }
1da177e4 2000
f801073f
DH
2001out:
2002 if (ret)
ae791a2d 2003 put_futex_key(&q->key);
f801073f
DH
2004 return ret;
2005}
2006
b41277dc
DH
2007static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
2008 ktime_t *abs_time, u32 bitset)
f801073f
DH
2009{
2010 struct hrtimer_sleeper timeout, *to = NULL;
f801073f
DH
2011 struct restart_block *restart;
2012 struct futex_hash_bucket *hb;
5bdb05f9 2013 struct futex_q q = futex_q_init;
f801073f
DH
2014 int ret;
2015
2016 if (!bitset)
2017 return -EINVAL;
f801073f
DH
2018 q.bitset = bitset;
2019
2020 if (abs_time) {
2021 to = &timeout;
2022
b41277dc
DH
2023 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2024 CLOCK_REALTIME : CLOCK_MONOTONIC,
2025 HRTIMER_MODE_ABS);
f801073f
DH
2026 hrtimer_init_sleeper(to, current);
2027 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2028 current->timer_slack_ns);
2029 }
2030
d58e6576 2031retry:
7ada876a
DH
2032 /*
2033 * Prepare to wait on uaddr. On success, holds hb lock and increments
2034 * q.key refs.
2035 */
b41277dc 2036 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
f801073f
DH
2037 if (ret)
2038 goto out;
2039
ca5f9524 2040 /* queue_me and wait for wakeup, timeout, or a signal. */
f1a11e05 2041 futex_wait_queue_me(hb, &q, to);
1da177e4
LT
2042
2043 /* If we were woken (and unqueued), we succeeded, whatever. */
2fff78c7 2044 ret = 0;
7ada876a 2045 /* unqueue_me() drops q.key ref */
1da177e4 2046 if (!unqueue_me(&q))
7ada876a 2047 goto out;
2fff78c7 2048 ret = -ETIMEDOUT;
ca5f9524 2049 if (to && !to->task)
7ada876a 2050 goto out;
72c1bbf3 2051
e2970f2f 2052 /*
d58e6576
TG
2053 * We expect signal_pending(current), but we might be the
2054 * victim of a spurious wakeup as well.
e2970f2f 2055 */
7ada876a 2056 if (!signal_pending(current))
d58e6576 2057 goto retry;
d58e6576 2058
2fff78c7 2059 ret = -ERESTARTSYS;
c19384b5 2060 if (!abs_time)
7ada876a 2061 goto out;
1da177e4 2062
2fff78c7
PZ
2063 restart = &current_thread_info()->restart_block;
2064 restart->fn = futex_wait_restart;
a3c74c52 2065 restart->futex.uaddr = uaddr;
2fff78c7
PZ
2066 restart->futex.val = val;
2067 restart->futex.time = abs_time->tv64;
2068 restart->futex.bitset = bitset;
0cd9c649 2069 restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
42d35d48 2070
2fff78c7
PZ
2071 ret = -ERESTART_RESTARTBLOCK;
2072
42d35d48 2073out:
ca5f9524
DH
2074 if (to) {
2075 hrtimer_cancel(&to->timer);
2076 destroy_hrtimer_on_stack(&to->timer);
2077 }
c87e2837
IM
2078 return ret;
2079}
2080
72c1bbf3
NP
2081
2082static long futex_wait_restart(struct restart_block *restart)
2083{
a3c74c52 2084 u32 __user *uaddr = restart->futex.uaddr;
a72188d8 2085 ktime_t t, *tp = NULL;
72c1bbf3 2086
a72188d8
DH
2087 if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
2088 t.tv64 = restart->futex.time;
2089 tp = &t;
2090 }
72c1bbf3 2091 restart->fn = do_no_restart_syscall;
b41277dc
DH
2092
2093 return (long)futex_wait(uaddr, restart->futex.flags,
2094 restart->futex.val, tp, restart->futex.bitset);
72c1bbf3
NP
2095}
2096
2097
c87e2837
IM
2098/*
2099 * Userspace tried a 0 -> TID atomic transition of the futex value
2100 * and failed. The kernel side here does the whole locking operation:
2101 * if there are waiters then it will block, it does PI, etc. (Due to
2102 * races the kernel might see a 0 value of the futex too.)
2103 */
b41277dc
DH
2104static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect,
2105 ktime_t *time, int trylock)
c87e2837 2106{
c5780e97 2107 struct hrtimer_sleeper timeout, *to = NULL;
c87e2837 2108 struct futex_hash_bucket *hb;
5bdb05f9 2109 struct futex_q q = futex_q_init;
dd973998 2110 int res, ret;
c87e2837
IM
2111
2112 if (refill_pi_state_cache())
2113 return -ENOMEM;
2114
c19384b5 2115 if (time) {
c5780e97 2116 to = &timeout;
237fc6e7
TG
2117 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
2118 HRTIMER_MODE_ABS);
c5780e97 2119 hrtimer_init_sleeper(to, current);
cc584b21 2120 hrtimer_set_expires(&to->timer, *time);
c5780e97
TG
2121 }
2122
42d35d48 2123retry:
9ea71503 2124 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
c87e2837 2125 if (unlikely(ret != 0))
42d35d48 2126 goto out;
c87e2837 2127
e4dc5b7a 2128retry_private:
82af7aca 2129 hb = queue_lock(&q);
c87e2837 2130
bab5bc9e 2131 ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
c87e2837 2132 if (unlikely(ret)) {
778e9a9c 2133 switch (ret) {
1a52084d
DH
2134 case 1:
2135 /* We got the lock. */
2136 ret = 0;
2137 goto out_unlock_put_key;
2138 case -EFAULT:
2139 goto uaddr_faulted;
778e9a9c
AK
2140 case -EAGAIN:
2141 /*
2142 * Task is exiting and we just wait for the
2143 * exit to complete.
2144 */
0d00c7b2 2145 queue_unlock(hb);
ae791a2d 2146 put_futex_key(&q.key);
778e9a9c
AK
2147 cond_resched();
2148 goto retry;
778e9a9c 2149 default:
42d35d48 2150 goto out_unlock_put_key;
c87e2837 2151 }
c87e2837
IM
2152 }
2153
2154 /*
2155 * Only actually queue now that the atomic ops are done:
2156 */
82af7aca 2157 queue_me(&q, hb);
c87e2837 2158
c87e2837
IM
2159 WARN_ON(!q.pi_state);
2160 /*
2161 * Block on the PI mutex:
2162 */
2163 if (!trylock)
2164 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
2165 else {
2166 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
2167 /* Fixup the trylock return value: */
2168 ret = ret ? 0 : -EWOULDBLOCK;
2169 }
2170
a99e4e41 2171 spin_lock(q.lock_ptr);
dd973998
DH
2172 /*
2173 * Fixup the pi_state owner and possibly acquire the lock if we
2174 * haven't already.
2175 */
ae791a2d 2176 res = fixup_owner(uaddr, &q, !ret);
dd973998
DH
2177 /*
2178 * If fixup_owner() returned an error, proprogate that. If it acquired
2179 * the lock, clear our -ETIMEDOUT or -EINTR.
2180 */
2181 if (res)
2182 ret = (res < 0) ? res : 0;
c87e2837 2183
e8f6386c 2184 /*
dd973998
DH
2185 * If fixup_owner() faulted and was unable to handle the fault, unlock
2186 * it and return the fault to userspace.
e8f6386c
DH
2187 */
2188 if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
2189 rt_mutex_unlock(&q.pi_state->pi_mutex);
2190
778e9a9c
AK
2191 /* Unqueue and drop the lock */
2192 unqueue_me_pi(&q);
c87e2837 2193
5ecb01cf 2194 goto out_put_key;
c87e2837 2195
42d35d48 2196out_unlock_put_key:
0d00c7b2 2197 queue_unlock(hb);
c87e2837 2198
42d35d48 2199out_put_key:
ae791a2d 2200 put_futex_key(&q.key);
42d35d48 2201out:
237fc6e7
TG
2202 if (to)
2203 destroy_hrtimer_on_stack(&to->timer);
dd973998 2204 return ret != -EINTR ? ret : -ERESTARTNOINTR;
c87e2837 2205
42d35d48 2206uaddr_faulted:
0d00c7b2 2207 queue_unlock(hb);
778e9a9c 2208
d0725992 2209 ret = fault_in_user_writeable(uaddr);
e4dc5b7a
DH
2210 if (ret)
2211 goto out_put_key;
c87e2837 2212
b41277dc 2213 if (!(flags & FLAGS_SHARED))
e4dc5b7a
DH
2214 goto retry_private;
2215
ae791a2d 2216 put_futex_key(&q.key);
e4dc5b7a 2217 goto retry;
c87e2837
IM
2218}
2219
c87e2837
IM
2220/*
2221 * Userspace attempted a TID -> 0 atomic transition, and failed.
2222 * This is the in-kernel slowpath: we look up the PI state (if any),
2223 * and do the rt-mutex unlock.
2224 */
b41277dc 2225static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
c87e2837
IM
2226{
2227 struct futex_hash_bucket *hb;
2228 struct futex_q *this, *next;
38d47c1b 2229 union futex_key key = FUTEX_KEY_INIT;
c0c9ed15 2230 u32 uval, vpid = task_pid_vnr(current);
e4dc5b7a 2231 int ret;
c87e2837
IM
2232
2233retry:
2234 if (get_user(uval, uaddr))
2235 return -EFAULT;
2236 /*
2237 * We release only a lock we actually own:
2238 */
c0c9ed15 2239 if ((uval & FUTEX_TID_MASK) != vpid)
c87e2837 2240 return -EPERM;
c87e2837 2241
9ea71503 2242 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
c87e2837
IM
2243 if (unlikely(ret != 0))
2244 goto out;
2245
2246 hb = hash_futex(&key);
2247 spin_lock(&hb->lock);
2248
c87e2837
IM
2249 /*
2250 * To avoid races, try to do the TID -> 0 atomic transition
2251 * again. If it succeeds then we can return without waking
2252 * anyone else up:
2253 */
37a9d912
ML
2254 if (!(uval & FUTEX_OWNER_DIED) &&
2255 cmpxchg_futex_value_locked(&uval, uaddr, vpid, 0))
c87e2837
IM
2256 goto pi_faulted;
2257 /*
2258 * Rare case: we managed to release the lock atomically,
2259 * no need to wake anyone else up:
2260 */
c0c9ed15 2261 if (unlikely(uval == vpid))
c87e2837
IM
2262 goto out_unlock;
2263
2264 /*
2265 * Ok, other tasks may need to be woken up - check waiters
2266 * and do the wakeup if necessary:
2267 */
0d00c7b2 2268 plist_for_each_entry_safe(this, next, &hb->chain, list) {
c87e2837
IM
2269 if (!match_futex (&this->key, &key))
2270 continue;
2271 ret = wake_futex_pi(uaddr, uval, this);
2272 /*
2273 * The atomic access to the futex value
2274 * generated a pagefault, so retry the
2275 * user-access and the wakeup:
2276 */
2277 if (ret == -EFAULT)
2278 goto pi_faulted;
2279 goto out_unlock;
2280 }
2281 /*
2282 * No waiters - kernel unlocks the futex:
2283 */
e3f2ddea
IM
2284 if (!(uval & FUTEX_OWNER_DIED)) {
2285 ret = unlock_futex_pi(uaddr, uval);
2286 if (ret == -EFAULT)
2287 goto pi_faulted;
2288 }
c87e2837
IM
2289
2290out_unlock:
2291 spin_unlock(&hb->lock);
ae791a2d 2292 put_futex_key(&key);
c87e2837 2293
42d35d48 2294out:
c87e2837
IM
2295 return ret;
2296
2297pi_faulted:
778e9a9c 2298 spin_unlock(&hb->lock);
ae791a2d 2299 put_futex_key(&key);
c87e2837 2300
d0725992 2301 ret = fault_in_user_writeable(uaddr);
b5686363 2302 if (!ret)
c87e2837
IM
2303 goto retry;
2304
1da177e4
LT
2305 return ret;
2306}
2307
52400ba9
DH
2308/**
2309 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2310 * @hb: the hash_bucket futex_q was original enqueued on
2311 * @q: the futex_q woken while waiting to be requeued
2312 * @key2: the futex_key of the requeue target futex
2313 * @timeout: the timeout associated with the wait (NULL if none)
2314 *
2315 * Detect if the task was woken on the initial futex as opposed to the requeue
2316 * target futex. If so, determine if it was a timeout or a signal that caused
2317 * the wakeup and return the appropriate error code to the caller. Must be
2318 * called with the hb lock held.
2319 *
6c23cbbd
RD
2320 * Return:
2321 * 0 = no early wakeup detected;
2322 * <0 = -ETIMEDOUT or -ERESTARTNOINTR
52400ba9
DH
2323 */
2324static inline
2325int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2326 struct futex_q *q, union futex_key *key2,
2327 struct hrtimer_sleeper *timeout)
2328{
2329 int ret = 0;
2330
2331 /*
2332 * With the hb lock held, we avoid races while we process the wakeup.
2333 * We only need to hold hb (and not hb2) to ensure atomicity as the
2334 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2335 * It can't be requeued from uaddr2 to something else since we don't
2336 * support a PI aware source futex for requeue.
2337 */
2338 if (!match_futex(&q->key, key2)) {
2339 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2340 /*
2341 * We were woken prior to requeue by a timeout or a signal.
2342 * Unqueue the futex_q and determine which it was.
2343 */
2e12978a 2344 plist_del(&q->list, &hb->chain);
52400ba9 2345
d58e6576 2346 /* Handle spurious wakeups gracefully */
11df6ddd 2347 ret = -EWOULDBLOCK;
52400ba9
DH
2348 if (timeout && !timeout->task)
2349 ret = -ETIMEDOUT;
d58e6576 2350 else if (signal_pending(current))
1c840c14 2351 ret = -ERESTARTNOINTR;
52400ba9
DH
2352 }
2353 return ret;
2354}
2355
2356/**
2357 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
56ec1607 2358 * @uaddr: the futex we initially wait on (non-pi)
b41277dc 2359 * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
52400ba9
DH
2360 * the same type, no requeueing from private to shared, etc.
2361 * @val: the expected value of uaddr
2362 * @abs_time: absolute timeout
56ec1607 2363 * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
52400ba9
DH
2364 * @uaddr2: the pi futex we will take prior to returning to user-space
2365 *
2366 * The caller will wait on uaddr and will be requeued by futex_requeue() to
6f7b0a2a
DH
2367 * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
2368 * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
2369 * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
2370 * without one, the pi logic would not know which task to boost/deboost, if
2371 * there was a need to.
52400ba9
DH
2372 *
2373 * We call schedule in futex_wait_queue_me() when we enqueue and return there
6c23cbbd 2374 * via the following--
52400ba9 2375 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
cc6db4e6
DH
2376 * 2) wakeup on uaddr2 after a requeue
2377 * 3) signal
2378 * 4) timeout
52400ba9 2379 *
cc6db4e6 2380 * If 3, cleanup and return -ERESTARTNOINTR.
52400ba9
DH
2381 *
2382 * If 2, we may then block on trying to take the rt_mutex and return via:
2383 * 5) successful lock
2384 * 6) signal
2385 * 7) timeout
2386 * 8) other lock acquisition failure
2387 *
cc6db4e6 2388 * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
52400ba9
DH
2389 *
2390 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2391 *
6c23cbbd
RD
2392 * Return:
2393 * 0 - On success;
52400ba9
DH
2394 * <0 - On error
2395 */
b41277dc 2396static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
52400ba9 2397 u32 val, ktime_t *abs_time, u32 bitset,
b41277dc 2398 u32 __user *uaddr2)
52400ba9
DH
2399{
2400 struct hrtimer_sleeper timeout, *to = NULL;
2401 struct rt_mutex_waiter rt_waiter;
2402 struct rt_mutex *pi_mutex = NULL;
52400ba9 2403 struct futex_hash_bucket *hb;
5bdb05f9
DH
2404 union futex_key key2 = FUTEX_KEY_INIT;
2405 struct futex_q q = futex_q_init;
52400ba9 2406 int res, ret;
52400ba9 2407
6f7b0a2a
DH
2408 if (uaddr == uaddr2)
2409 return -EINVAL;
2410
52400ba9
DH
2411 if (!bitset)
2412 return -EINVAL;
2413
2414 if (abs_time) {
2415 to = &timeout;
b41277dc
DH
2416 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2417 CLOCK_REALTIME : CLOCK_MONOTONIC,
2418 HRTIMER_MODE_ABS);
52400ba9
DH
2419 hrtimer_init_sleeper(to, current);
2420 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2421 current->timer_slack_ns);
2422 }
2423
2424 /*
2425 * The waiter is allocated on our stack, manipulated by the requeue
2426 * code while we sleep on uaddr.
2427 */
2428 debug_rt_mutex_init_waiter(&rt_waiter);
fb00aca4
PZ
2429 RB_CLEAR_NODE(&rt_waiter.pi_tree_entry);
2430 RB_CLEAR_NODE(&rt_waiter.tree_entry);
52400ba9
DH
2431 rt_waiter.task = NULL;
2432
9ea71503 2433 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
52400ba9
DH
2434 if (unlikely(ret != 0))
2435 goto out;
2436
84bc4af5
DH
2437 q.bitset = bitset;
2438 q.rt_waiter = &rt_waiter;
2439 q.requeue_pi_key = &key2;
2440
7ada876a
DH
2441 /*
2442 * Prepare to wait on uaddr. On success, increments q.key (key1) ref
2443 * count.
2444 */
b41277dc 2445 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
c8b15a70
TG
2446 if (ret)
2447 goto out_key2;
52400ba9
DH
2448
2449 /* Queue the futex_q, drop the hb lock, wait for wakeup. */
f1a11e05 2450 futex_wait_queue_me(hb, &q, to);
52400ba9
DH
2451
2452 spin_lock(&hb->lock);
2453 ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2454 spin_unlock(&hb->lock);
2455 if (ret)
2456 goto out_put_keys;
2457
2458 /*
2459 * In order for us to be here, we know our q.key == key2, and since
2460 * we took the hb->lock above, we also know that futex_requeue() has
2461 * completed and we no longer have to concern ourselves with a wakeup
7ada876a
DH
2462 * race with the atomic proxy lock acquisition by the requeue code. The
2463 * futex_requeue dropped our key1 reference and incremented our key2
2464 * reference count.
52400ba9
DH
2465 */
2466
2467 /* Check if the requeue code acquired the second futex for us. */
2468 if (!q.rt_waiter) {
2469 /*
2470 * Got the lock. We might not be the anticipated owner if we
2471 * did a lock-steal - fix up the PI-state in that case.
2472 */
2473 if (q.pi_state && (q.pi_state->owner != current)) {
2474 spin_lock(q.lock_ptr);
ae791a2d 2475 ret = fixup_pi_state_owner(uaddr2, &q, current);
52400ba9
DH
2476 spin_unlock(q.lock_ptr);
2477 }
2478 } else {
2479 /*
2480 * We have been woken up by futex_unlock_pi(), a timeout, or a
2481 * signal. futex_unlock_pi() will not destroy the lock_ptr nor
2482 * the pi_state.
2483 */
f27071cb 2484 WARN_ON(!q.pi_state);
52400ba9
DH
2485 pi_mutex = &q.pi_state->pi_mutex;
2486 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
2487 debug_rt_mutex_free_waiter(&rt_waiter);
2488
2489 spin_lock(q.lock_ptr);
2490 /*
2491 * Fixup the pi_state owner and possibly acquire the lock if we
2492 * haven't already.
2493 */
ae791a2d 2494 res = fixup_owner(uaddr2, &q, !ret);
52400ba9
DH
2495 /*
2496 * If fixup_owner() returned an error, proprogate that. If it
56ec1607 2497 * acquired the lock, clear -ETIMEDOUT or -EINTR.
52400ba9
DH
2498 */
2499 if (res)
2500 ret = (res < 0) ? res : 0;
2501
2502 /* Unqueue and drop the lock. */
2503 unqueue_me_pi(&q);
2504 }
2505
2506 /*
2507 * If fixup_pi_state_owner() faulted and was unable to handle the
2508 * fault, unlock the rt_mutex and return the fault to userspace.
2509 */
2510 if (ret == -EFAULT) {
b6070a8d 2511 if (pi_mutex && rt_mutex_owner(pi_mutex) == current)
52400ba9
DH
2512 rt_mutex_unlock(pi_mutex);
2513 } else if (ret == -EINTR) {
52400ba9 2514 /*
cc6db4e6
DH
2515 * We've already been requeued, but cannot restart by calling
2516 * futex_lock_pi() directly. We could restart this syscall, but
2517 * it would detect that the user space "val" changed and return
2518 * -EWOULDBLOCK. Save the overhead of the restart and return
2519 * -EWOULDBLOCK directly.
52400ba9 2520 */
2070887f 2521 ret = -EWOULDBLOCK;
52400ba9
DH
2522 }
2523
2524out_put_keys:
ae791a2d 2525 put_futex_key(&q.key);
c8b15a70 2526out_key2:
ae791a2d 2527 put_futex_key(&key2);
52400ba9
DH
2528
2529out:
2530 if (to) {
2531 hrtimer_cancel(&to->timer);
2532 destroy_hrtimer_on_stack(&to->timer);
2533 }
2534 return ret;
2535}
2536
0771dfef
IM
2537/*
2538 * Support for robust futexes: the kernel cleans up held futexes at
2539 * thread exit time.
2540 *
2541 * Implementation: user-space maintains a per-thread list of locks it
2542 * is holding. Upon do_exit(), the kernel carefully walks this list,
2543 * and marks all locks that are owned by this thread with the
c87e2837 2544 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
0771dfef
IM
2545 * always manipulated with the lock held, so the list is private and
2546 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2547 * field, to allow the kernel to clean up if the thread dies after
2548 * acquiring the lock, but just before it could have added itself to
2549 * the list. There can only be one such pending lock.
2550 */
2551
2552/**
d96ee56c
DH
2553 * sys_set_robust_list() - Set the robust-futex list head of a task
2554 * @head: pointer to the list-head
2555 * @len: length of the list-head, as userspace expects
0771dfef 2556 */
836f92ad
HC
2557SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2558 size_t, len)
0771dfef 2559{
a0c1e907
TG
2560 if (!futex_cmpxchg_enabled)
2561 return -ENOSYS;
0771dfef
IM
2562 /*
2563 * The kernel knows only one size for now:
2564 */
2565 if (unlikely(len != sizeof(*head)))
2566 return -EINVAL;
2567
2568 current->robust_list = head;
2569
2570 return 0;
2571}
2572
2573/**
d96ee56c
DH
2574 * sys_get_robust_list() - Get the robust-futex list head of a task
2575 * @pid: pid of the process [zero for current task]
2576 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
2577 * @len_ptr: pointer to a length field, the kernel fills in the header size
0771dfef 2578 */
836f92ad
HC
2579SYSCALL_DEFINE3(get_robust_list, int, pid,
2580 struct robust_list_head __user * __user *, head_ptr,
2581 size_t __user *, len_ptr)
0771dfef 2582{
ba46df98 2583 struct robust_list_head __user *head;
0771dfef 2584 unsigned long ret;
bdbb776f 2585 struct task_struct *p;
0771dfef 2586
a0c1e907
TG
2587 if (!futex_cmpxchg_enabled)
2588 return -ENOSYS;
2589
bdbb776f
KC
2590 rcu_read_lock();
2591
2592 ret = -ESRCH;
0771dfef 2593 if (!pid)
bdbb776f 2594 p = current;
0771dfef 2595 else {
228ebcbe 2596 p = find_task_by_vpid(pid);
0771dfef
IM
2597 if (!p)
2598 goto err_unlock;
0771dfef
IM
2599 }
2600
bdbb776f
KC
2601 ret = -EPERM;
2602 if (!ptrace_may_access(p, PTRACE_MODE_READ))
2603 goto err_unlock;
2604
2605 head = p->robust_list;
2606 rcu_read_unlock();
2607
0771dfef
IM
2608 if (put_user(sizeof(*head), len_ptr))
2609 return -EFAULT;
2610 return put_user(head, head_ptr);
2611
2612err_unlock:
aaa2a97e 2613 rcu_read_unlock();
0771dfef
IM
2614
2615 return ret;
2616}
2617
2618/*
2619 * Process a futex-list entry, check whether it's owned by the
2620 * dying task, and do notification if so:
2621 */
e3f2ddea 2622int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
0771dfef 2623{
7cfdaf38 2624 u32 uval, uninitialized_var(nval), mval;
0771dfef 2625
8f17d3a5
IM
2626retry:
2627 if (get_user(uval, uaddr))
0771dfef
IM
2628 return -1;
2629
b488893a 2630 if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
0771dfef
IM
2631 /*
2632 * Ok, this dying thread is truly holding a futex
2633 * of interest. Set the OWNER_DIED bit atomically
2634 * via cmpxchg, and if the value had FUTEX_WAITERS
2635 * set, wake up a waiter (if any). (We have to do a
2636 * futex_wake() even if OWNER_DIED is already set -
2637 * to handle the rare but possible case of recursive
2638 * thread-death.) The rest of the cleanup is done in
2639 * userspace.
2640 */
e3f2ddea 2641 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
6e0aa9f8
TG
2642 /*
2643 * We are not holding a lock here, but we want to have
2644 * the pagefault_disable/enable() protection because
2645 * we want to handle the fault gracefully. If the
2646 * access fails we try to fault in the futex with R/W
2647 * verification via get_user_pages. get_user() above
2648 * does not guarantee R/W access. If that fails we
2649 * give up and leave the futex locked.
2650 */
2651 if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
2652 if (fault_in_user_writeable(uaddr))
2653 return -1;
2654 goto retry;
2655 }
c87e2837 2656 if (nval != uval)
8f17d3a5 2657 goto retry;
0771dfef 2658
e3f2ddea
IM
2659 /*
2660 * Wake robust non-PI futexes here. The wakeup of
2661 * PI futexes happens in exit_pi_state():
2662 */
36cf3b5c 2663 if (!pi && (uval & FUTEX_WAITERS))
c2f9f201 2664 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
0771dfef
IM
2665 }
2666 return 0;
2667}
2668
e3f2ddea
IM
2669/*
2670 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
2671 */
2672static inline int fetch_robust_entry(struct robust_list __user **entry,
ba46df98 2673 struct robust_list __user * __user *head,
1dcc41bb 2674 unsigned int *pi)
e3f2ddea
IM
2675{
2676 unsigned long uentry;
2677
ba46df98 2678 if (get_user(uentry, (unsigned long __user *)head))
e3f2ddea
IM
2679 return -EFAULT;
2680
ba46df98 2681 *entry = (void __user *)(uentry & ~1UL);
e3f2ddea
IM
2682 *pi = uentry & 1;
2683
2684 return 0;
2685}
2686
0771dfef
IM
2687/*
2688 * Walk curr->robust_list (very carefully, it's a userspace list!)
2689 * and mark any locks found there dead, and notify any waiters.
2690 *
2691 * We silently return on any sign of list-walking problem.
2692 */
2693void exit_robust_list(struct task_struct *curr)
2694{
2695 struct robust_list_head __user *head = curr->robust_list;
9f96cb1e 2696 struct robust_list __user *entry, *next_entry, *pending;
4c115e95
DH
2697 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
2698 unsigned int uninitialized_var(next_pi);
0771dfef 2699 unsigned long futex_offset;
9f96cb1e 2700 int rc;
0771dfef 2701
a0c1e907
TG
2702 if (!futex_cmpxchg_enabled)
2703 return;
2704
0771dfef
IM
2705 /*
2706 * Fetch the list head (which was registered earlier, via
2707 * sys_set_robust_list()):
2708 */
e3f2ddea 2709 if (fetch_robust_entry(&entry, &head->list.next, &pi))
0771dfef
IM
2710 return;
2711 /*
2712 * Fetch the relative futex offset:
2713 */
2714 if (get_user(futex_offset, &head->futex_offset))
2715 return;
2716 /*
2717 * Fetch any possibly pending lock-add first, and handle it
2718 * if it exists:
2719 */
e3f2ddea 2720 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
0771dfef 2721 return;
e3f2ddea 2722
9f96cb1e 2723 next_entry = NULL; /* avoid warning with gcc */
0771dfef 2724 while (entry != &head->list) {
9f96cb1e
MS
2725 /*
2726 * Fetch the next entry in the list before calling
2727 * handle_futex_death:
2728 */
2729 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
0771dfef
IM
2730 /*
2731 * A pending lock might already be on the list, so
c87e2837 2732 * don't process it twice:
0771dfef
IM
2733 */
2734 if (entry != pending)
ba46df98 2735 if (handle_futex_death((void __user *)entry + futex_offset,
e3f2ddea 2736 curr, pi))
0771dfef 2737 return;
9f96cb1e 2738 if (rc)
0771dfef 2739 return;
9f96cb1e
MS
2740 entry = next_entry;
2741 pi = next_pi;
0771dfef
IM
2742 /*
2743 * Avoid excessively long or circular lists:
2744 */
2745 if (!--limit)
2746 break;
2747
2748 cond_resched();
2749 }
9f96cb1e
MS
2750
2751 if (pending)
2752 handle_futex_death((void __user *)pending + futex_offset,
2753 curr, pip);
0771dfef
IM
2754}
2755
c19384b5 2756long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
e2970f2f 2757 u32 __user *uaddr2, u32 val2, u32 val3)
1da177e4 2758{
81b40539 2759 int cmd = op & FUTEX_CMD_MASK;
b41277dc 2760 unsigned int flags = 0;
34f01cc1
ED
2761
2762 if (!(op & FUTEX_PRIVATE_FLAG))
b41277dc 2763 flags |= FLAGS_SHARED;
1da177e4 2764
b41277dc
DH
2765 if (op & FUTEX_CLOCK_REALTIME) {
2766 flags |= FLAGS_CLOCKRT;
2767 if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
2768 return -ENOSYS;
2769 }
1da177e4 2770
59263b51
TG
2771 switch (cmd) {
2772 case FUTEX_LOCK_PI:
2773 case FUTEX_UNLOCK_PI:
2774 case FUTEX_TRYLOCK_PI:
2775 case FUTEX_WAIT_REQUEUE_PI:
2776 case FUTEX_CMP_REQUEUE_PI:
2777 if (!futex_cmpxchg_enabled)
2778 return -ENOSYS;
2779 }
2780
34f01cc1 2781 switch (cmd) {
1da177e4 2782 case FUTEX_WAIT:
cd689985
TG
2783 val3 = FUTEX_BITSET_MATCH_ANY;
2784 case FUTEX_WAIT_BITSET:
81b40539 2785 return futex_wait(uaddr, flags, val, timeout, val3);
1da177e4 2786 case FUTEX_WAKE:
cd689985
TG
2787 val3 = FUTEX_BITSET_MATCH_ANY;
2788 case FUTEX_WAKE_BITSET:
81b40539 2789 return futex_wake(uaddr, flags, val, val3);
1da177e4 2790 case FUTEX_REQUEUE:
81b40539 2791 return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
1da177e4 2792 case FUTEX_CMP_REQUEUE:
81b40539 2793 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
4732efbe 2794 case FUTEX_WAKE_OP:
81b40539 2795 return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
c87e2837 2796 case FUTEX_LOCK_PI:
81b40539 2797 return futex_lock_pi(uaddr, flags, val, timeout, 0);
c87e2837 2798 case FUTEX_UNLOCK_PI:
81b40539 2799 return futex_unlock_pi(uaddr, flags);
c87e2837 2800 case FUTEX_TRYLOCK_PI:
81b40539 2801 return futex_lock_pi(uaddr, flags, 0, timeout, 1);
52400ba9
DH
2802 case FUTEX_WAIT_REQUEUE_PI:
2803 val3 = FUTEX_BITSET_MATCH_ANY;
81b40539
TG
2804 return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
2805 uaddr2);
52400ba9 2806 case FUTEX_CMP_REQUEUE_PI:
81b40539 2807 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
1da177e4 2808 }
81b40539 2809 return -ENOSYS;
1da177e4
LT
2810}
2811
2812
17da2bd9
HC
2813SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
2814 struct timespec __user *, utime, u32 __user *, uaddr2,
2815 u32, val3)
1da177e4 2816{
c19384b5
PP
2817 struct timespec ts;
2818 ktime_t t, *tp = NULL;
e2970f2f 2819 u32 val2 = 0;
34f01cc1 2820 int cmd = op & FUTEX_CMD_MASK;
1da177e4 2821
cd689985 2822 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
52400ba9
DH
2823 cmd == FUTEX_WAIT_BITSET ||
2824 cmd == FUTEX_WAIT_REQUEUE_PI)) {
c19384b5 2825 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
1da177e4 2826 return -EFAULT;
c19384b5 2827 if (!timespec_valid(&ts))
9741ef96 2828 return -EINVAL;
c19384b5
PP
2829
2830 t = timespec_to_ktime(ts);
34f01cc1 2831 if (cmd == FUTEX_WAIT)
5a7780e7 2832 t = ktime_add_safe(ktime_get(), t);
c19384b5 2833 tp = &t;
1da177e4
LT
2834 }
2835 /*
52400ba9 2836 * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
f54f0986 2837 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
1da177e4 2838 */
f54f0986 2839 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
ba9c22f2 2840 cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
e2970f2f 2841 val2 = (u32) (unsigned long) utime;
1da177e4 2842
c19384b5 2843 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
1da177e4
LT
2844}
2845
f6d107fb 2846static int __init futex_init(void)
1da177e4 2847{
a0c1e907 2848 u32 curval;
63b1a816 2849 unsigned int futex_shift;
a52b89eb
DB
2850 unsigned long i;
2851
2852#if CONFIG_BASE_SMALL
2853 futex_hashsize = 16;
2854#else
2855 futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
2856#endif
2857
2858 futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
2859 futex_hashsize, 0,
2860 futex_hashsize < 256 ? HASH_SMALL : 0,
63b1a816
HC
2861 &futex_shift, NULL,
2862 futex_hashsize, futex_hashsize);
2863 futex_hashsize = 1UL << futex_shift;
a0c1e907
TG
2864 /*
2865 * This will fail and we want it. Some arch implementations do
2866 * runtime detection of the futex_atomic_cmpxchg_inatomic()
2867 * functionality. We want to know that before we call in any
2868 * of the complex code paths. Also we want to prevent
2869 * registration of robust lists in that case. NULL is
2870 * guaranteed to fault and we get -EFAULT on functional
fb62db2b 2871 * implementation, the non-functional ones will return
a0c1e907
TG
2872 * -ENOSYS.
2873 */
37a9d912 2874 if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
a0c1e907
TG
2875 futex_cmpxchg_enabled = 1;
2876
a52b89eb 2877 for (i = 0; i < futex_hashsize; i++) {
732375c6 2878 plist_head_init(&futex_queues[i].chain);
3e4ab747
TG
2879 spin_lock_init(&futex_queues[i].lock);
2880 }
2881
1da177e4
LT
2882 return 0;
2883}
f6d107fb 2884__initcall(futex_init);