]>
git.proxmox.com Git - mirror_ubuntu-focal-kernel.git/blob - net/unix/garbage.c
2 * NET3: Garbage Collector For AF_UNIX sockets
5 * Copyright (C) Barak A. Pearlmutter.
6 * Released under the GPL version 2 or later.
8 * Chopped about by Alan Cox 22/3/96 to make it fit the AF_UNIX socket problem.
9 * If it doesn't work blame me, it worked when Barak sent it.
16 * Current optimizations:
18 * - explicit stack instead of recursion
19 * - tail recurse on first born instead of immediate push/pop
20 * - we gather the stuff that should not be killed into tree
21 * and stack is just a path from root to the current pointer.
23 * Future optimizations:
25 * - don't just push entire root set; process in place
27 * This program is free software; you can redistribute it and/or
28 * modify it under the terms of the GNU General Public License
29 * as published by the Free Software Foundation; either version
30 * 2 of the License, or (at your option) any later version.
33 * Alan Cox 07 Sept 1997 Vmalloc internal stack as needed.
34 * Cope with changing max_files.
36 * Graph may have cycles. That is, we can send the descriptor
37 * of foo to bar and vice versa. Current code chokes on that.
38 * Fix: move SCM_RIGHTS ones into the separate list and then
39 * skb_free() them all instead of doing explicit fput's.
40 * Another problem: since fput() may block somebody may
41 * create a new unix_socket when we are in the middle of sweep
42 * phase. Fix: revert the logic wrt MARKED. Mark everything
43 * upon the beginning and unmark non-junk ones.
45 * [12 Oct 1998] AAARGH! New code purges all SCM_RIGHTS
46 * sent to connect()'ed but still not accept()'ed sockets.
47 * Fixed. Old code had slightly different problem here:
48 * extra fput() in situation when we passed the descriptor via
49 * such socket and closed it (descriptor). That would happen on
50 * each unix_gc() until the accept(). Since the struct file in
51 * question would go to the free list and might be reused...
52 * That might be the reason of random oopses on filp_close()
53 * in unrelated processes.
56 * Kill the explicit allocation of stack. Now we keep the tree
57 * with root in dummy + pointer (gc_current) to one of the nodes.
58 * Stack is represented as path from gc_current to dummy. Unmark
59 * now means "add to tree". Push == "make it a son of gc_current".
60 * Pop == "move gc_current to parent". We keep only pointers to
61 * parents (->gc_tree).
63 * Damn. Added missing check for ->dead in listen queues scanning.
65 * Miklos Szeredi 25 Jun 2007
66 * Reimplement with a cycle collecting algorithm. This should
67 * solve several problems with the previous code, like being racy
68 * wrt receive and holding up unrelated socket operations.
71 #include <linux/kernel.h>
72 #include <linux/string.h>
73 #include <linux/socket.h>
75 #include <linux/net.h>
77 #include <linux/skbuff.h>
78 #include <linux/netdevice.h>
79 #include <linux/file.h>
80 #include <linux/proc_fs.h>
81 #include <linux/mutex.h>
82 #include <linux/wait.h>
85 #include <net/af_unix.h>
87 #include <net/tcp_states.h>
89 /* Internal data structures and random procedures: */
91 static LIST_HEAD(gc_inflight_list
);
92 static LIST_HEAD(gc_candidates
);
93 static DEFINE_SPINLOCK(unix_gc_lock
);
94 static DECLARE_WAIT_QUEUE_HEAD(unix_gc_wait
);
96 unsigned int unix_tot_inflight
;
98 struct sock
*unix_get_socket(struct file
*filp
)
100 struct sock
*u_sock
= NULL
;
101 struct inode
*inode
= file_inode(filp
);
104 if (S_ISSOCK(inode
->i_mode
) && !(filp
->f_mode
& FMODE_PATH
)) {
105 struct socket
*sock
= SOCKET_I(inode
);
106 struct sock
*s
= sock
->sk
;
109 if (s
&& sock
->ops
&& sock
->ops
->family
== PF_UNIX
)
115 /* Keep the number of times in flight count for the file
116 * descriptor if it is for an AF_UNIX socket.
119 void unix_inflight(struct user_struct
*user
, struct file
*fp
)
121 struct sock
*s
= unix_get_socket(fp
);
123 spin_lock(&unix_gc_lock
);
126 struct unix_sock
*u
= unix_sk(s
);
128 if (atomic_long_inc_return(&u
->inflight
) == 1) {
129 BUG_ON(!list_empty(&u
->link
));
130 list_add_tail(&u
->link
, &gc_inflight_list
);
132 BUG_ON(list_empty(&u
->link
));
136 user
->unix_inflight
++;
137 spin_unlock(&unix_gc_lock
);
140 void unix_notinflight(struct user_struct
*user
, struct file
*fp
)
142 struct sock
*s
= unix_get_socket(fp
);
144 spin_lock(&unix_gc_lock
);
147 struct unix_sock
*u
= unix_sk(s
);
149 BUG_ON(list_empty(&u
->link
));
151 if (atomic_long_dec_and_test(&u
->inflight
))
152 list_del_init(&u
->link
);
155 user
->unix_inflight
--;
156 spin_unlock(&unix_gc_lock
);
159 static void scan_inflight(struct sock
*x
, void (*func
)(struct unix_sock
*),
160 struct sk_buff_head
*hitlist
)
163 struct sk_buff
*next
;
165 spin_lock(&x
->sk_receive_queue
.lock
);
166 skb_queue_walk_safe(&x
->sk_receive_queue
, skb
, next
) {
167 /* Do we have file descriptors ? */
168 if (UNIXCB(skb
).fp
) {
170 /* Process the descriptors of this socket */
171 int nfd
= UNIXCB(skb
).fp
->count
;
172 struct file
**fp
= UNIXCB(skb
).fp
->fp
;
175 /* Get the socket the fd matches if it indeed does so */
176 struct sock
*sk
= unix_get_socket(*fp
++);
179 struct unix_sock
*u
= unix_sk(sk
);
181 /* Ignore non-candidates, they could
182 * have been added to the queues after
183 * starting the garbage collection
185 if (test_bit(UNIX_GC_CANDIDATE
, &u
->gc_flags
)) {
192 if (hit
&& hitlist
!= NULL
) {
193 __skb_unlink(skb
, &x
->sk_receive_queue
);
194 __skb_queue_tail(hitlist
, skb
);
198 spin_unlock(&x
->sk_receive_queue
.lock
);
201 static void scan_children(struct sock
*x
, void (*func
)(struct unix_sock
*),
202 struct sk_buff_head
*hitlist
)
204 if (x
->sk_state
!= TCP_LISTEN
) {
205 scan_inflight(x
, func
, hitlist
);
208 struct sk_buff
*next
;
212 /* For a listening socket collect the queued embryos
213 * and perform a scan on them as well.
215 spin_lock(&x
->sk_receive_queue
.lock
);
216 skb_queue_walk_safe(&x
->sk_receive_queue
, skb
, next
) {
217 u
= unix_sk(skb
->sk
);
219 /* An embryo cannot be in-flight, so it's safe
220 * to use the list link.
222 BUG_ON(!list_empty(&u
->link
));
223 list_add_tail(&u
->link
, &embryos
);
225 spin_unlock(&x
->sk_receive_queue
.lock
);
227 while (!list_empty(&embryos
)) {
228 u
= list_entry(embryos
.next
, struct unix_sock
, link
);
229 scan_inflight(&u
->sk
, func
, hitlist
);
230 list_del_init(&u
->link
);
235 static void dec_inflight(struct unix_sock
*usk
)
237 atomic_long_dec(&usk
->inflight
);
240 static void inc_inflight(struct unix_sock
*usk
)
242 atomic_long_inc(&usk
->inflight
);
245 static void inc_inflight_move_tail(struct unix_sock
*u
)
247 atomic_long_inc(&u
->inflight
);
248 /* If this still might be part of a cycle, move it to the end
249 * of the list, so that it's checked even if it was already
252 if (test_bit(UNIX_GC_MAYBE_CYCLE
, &u
->gc_flags
))
253 list_move_tail(&u
->link
, &gc_candidates
);
256 static bool gc_in_progress
;
257 #define UNIX_INFLIGHT_TRIGGER_GC 16000
259 void wait_for_unix_gc(void)
261 /* If number of inflight sockets is insane,
262 * force a garbage collect right now.
264 if (unix_tot_inflight
> UNIX_INFLIGHT_TRIGGER_GC
&& !gc_in_progress
)
266 wait_event(unix_gc_wait
, gc_in_progress
== false);
269 /* The external entry point: unix_gc() */
273 struct unix_sock
*next
;
274 struct sk_buff_head hitlist
;
275 struct list_head cursor
;
276 LIST_HEAD(not_cycle_list
);
278 spin_lock(&unix_gc_lock
);
280 /* Avoid a recursive GC. */
284 gc_in_progress
= true;
285 /* First, select candidates for garbage collection. Only
286 * in-flight sockets are considered, and from those only ones
287 * which don't have any external reference.
289 * Holding unix_gc_lock will protect these candidates from
290 * being detached, and hence from gaining an external
291 * reference. Since there are no possible receivers, all
292 * buffers currently on the candidates' queues stay there
293 * during the garbage collection.
295 * We also know that no new candidate can be added onto the
296 * receive queues. Other, non candidate sockets _can_ be
297 * added to queue, so we must make sure only to touch
300 list_for_each_entry_safe(u
, next
, &gc_inflight_list
, link
) {
304 total_refs
= file_count(u
->sk
.sk_socket
->file
);
305 inflight_refs
= atomic_long_read(&u
->inflight
);
307 BUG_ON(inflight_refs
< 1);
308 BUG_ON(total_refs
< inflight_refs
);
309 if (total_refs
== inflight_refs
) {
310 list_move_tail(&u
->link
, &gc_candidates
);
311 __set_bit(UNIX_GC_CANDIDATE
, &u
->gc_flags
);
312 __set_bit(UNIX_GC_MAYBE_CYCLE
, &u
->gc_flags
);
316 /* Now remove all internal in-flight reference to children of
319 list_for_each_entry(u
, &gc_candidates
, link
)
320 scan_children(&u
->sk
, dec_inflight
, NULL
);
322 /* Restore the references for children of all candidates,
323 * which have remaining references. Do this recursively, so
324 * only those remain, which form cyclic references.
326 * Use a "cursor" link, to make the list traversal safe, even
327 * though elements might be moved about.
329 list_add(&cursor
, &gc_candidates
);
330 while (cursor
.next
!= &gc_candidates
) {
331 u
= list_entry(cursor
.next
, struct unix_sock
, link
);
333 /* Move cursor to after the current position. */
334 list_move(&cursor
, &u
->link
);
336 if (atomic_long_read(&u
->inflight
) > 0) {
337 list_move_tail(&u
->link
, ¬_cycle_list
);
338 __clear_bit(UNIX_GC_MAYBE_CYCLE
, &u
->gc_flags
);
339 scan_children(&u
->sk
, inc_inflight_move_tail
, NULL
);
344 /* not_cycle_list contains those sockets which do not make up a
345 * cycle. Restore these to the inflight list.
347 while (!list_empty(¬_cycle_list
)) {
348 u
= list_entry(not_cycle_list
.next
, struct unix_sock
, link
);
349 __clear_bit(UNIX_GC_CANDIDATE
, &u
->gc_flags
);
350 list_move_tail(&u
->link
, &gc_inflight_list
);
353 /* Now gc_candidates contains only garbage. Restore original
354 * inflight counters for these as well, and remove the skbuffs
355 * which are creating the cycle(s).
357 skb_queue_head_init(&hitlist
);
358 list_for_each_entry(u
, &gc_candidates
, link
)
359 scan_children(&u
->sk
, inc_inflight
, &hitlist
);
361 spin_unlock(&unix_gc_lock
);
363 /* Here we are. Hitlist is filled. Die. */
364 __skb_queue_purge(&hitlist
);
366 spin_lock(&unix_gc_lock
);
368 /* All candidates should have been detached by now. */
369 BUG_ON(!list_empty(&gc_candidates
));
370 gc_in_progress
= false;
371 wake_up(&unix_gc_wait
);
374 spin_unlock(&unix_gc_lock
);