2 * Read-Copy Update mechanism for mutual exclusion
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, you can access it online at
16 * http://www.gnu.org/licenses/gpl-2.0.html.
18 * Copyright IBM Corporation, 2001
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
23 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
24 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
26 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
27 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
29 * For detailed explanation of Read-Copy Update mechanism see -
30 * http://lse.sourceforge.net/locking/rcupdate.html
33 #include <linux/types.h>
34 #include <linux/kernel.h>
35 #include <linux/init.h>
36 #include <linux/spinlock.h>
37 #include <linux/smp.h>
38 #include <linux/interrupt.h>
39 #include <linux/sched.h>
40 #include <linux/atomic.h>
41 #include <linux/bitops.h>
42 #include <linux/percpu.h>
43 #include <linux/notifier.h>
44 #include <linux/cpu.h>
45 #include <linux/mutex.h>
46 #include <linux/export.h>
47 #include <linux/hardirq.h>
48 #include <linux/delay.h>
49 #include <linux/module.h>
51 #define CREATE_TRACE_POINTS
55 MODULE_ALIAS("rcupdate");
56 #ifdef MODULE_PARAM_PREFIX
57 #undef MODULE_PARAM_PREFIX
59 #define MODULE_PARAM_PREFIX "rcupdate."
61 module_param(rcu_expedited
, int, 0);
63 #ifdef CONFIG_PREEMPT_RCU
66 * Preemptible RCU implementation for rcu_read_lock().
67 * Just increment ->rcu_read_lock_nesting, shared state will be updated
70 void __rcu_read_lock(void)
72 current
->rcu_read_lock_nesting
++;
73 barrier(); /* critical section after entry code. */
75 EXPORT_SYMBOL_GPL(__rcu_read_lock
);
78 * Preemptible RCU implementation for rcu_read_unlock().
79 * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
80 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
81 * invoke rcu_read_unlock_special() to clean up after a context switch
82 * in an RCU read-side critical section and other special cases.
84 void __rcu_read_unlock(void)
86 struct task_struct
*t
= current
;
88 if (t
->rcu_read_lock_nesting
!= 1) {
89 --t
->rcu_read_lock_nesting
;
91 barrier(); /* critical section before exit code. */
92 t
->rcu_read_lock_nesting
= INT_MIN
;
93 barrier(); /* assign before ->rcu_read_unlock_special load */
94 if (unlikely(ACCESS_ONCE(t
->rcu_read_unlock_special
)))
95 rcu_read_unlock_special(t
);
96 barrier(); /* ->rcu_read_unlock_special load before assign */
97 t
->rcu_read_lock_nesting
= 0;
99 #ifdef CONFIG_PROVE_LOCKING
101 int rrln
= ACCESS_ONCE(t
->rcu_read_lock_nesting
);
103 WARN_ON_ONCE(rrln
< 0 && rrln
> INT_MIN
/ 2);
105 #endif /* #ifdef CONFIG_PROVE_LOCKING */
107 EXPORT_SYMBOL_GPL(__rcu_read_unlock
);
109 #endif /* #ifdef CONFIG_PREEMPT_RCU */
111 #ifdef CONFIG_DEBUG_LOCK_ALLOC
112 static struct lock_class_key rcu_lock_key
;
113 struct lockdep_map rcu_lock_map
=
114 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key
);
115 EXPORT_SYMBOL_GPL(rcu_lock_map
);
117 static struct lock_class_key rcu_bh_lock_key
;
118 struct lockdep_map rcu_bh_lock_map
=
119 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key
);
120 EXPORT_SYMBOL_GPL(rcu_bh_lock_map
);
122 static struct lock_class_key rcu_sched_lock_key
;
123 struct lockdep_map rcu_sched_lock_map
=
124 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key
);
125 EXPORT_SYMBOL_GPL(rcu_sched_lock_map
);
127 static struct lock_class_key rcu_callback_key
;
128 struct lockdep_map rcu_callback_map
=
129 STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key
);
130 EXPORT_SYMBOL_GPL(rcu_callback_map
);
132 int notrace
debug_lockdep_rcu_enabled(void)
134 return rcu_scheduler_active
&& debug_locks
&&
135 current
->lockdep_recursion
== 0;
137 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled
);
140 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
142 * Check for bottom half being disabled, which covers both the
143 * CONFIG_PROVE_RCU and not cases. Note that if someone uses
144 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
145 * will show the situation. This is useful for debug checks in functions
146 * that require that they be called within an RCU read-side critical
149 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
151 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
152 * offline from an RCU perspective, so check for those as well.
154 int rcu_read_lock_bh_held(void)
156 if (!debug_lockdep_rcu_enabled())
158 if (!rcu_is_watching())
160 if (!rcu_lockdep_current_cpu_online())
162 return in_softirq() || irqs_disabled();
164 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held
);
166 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
168 struct rcu_synchronize
{
169 struct rcu_head head
;
170 struct completion completion
;
174 * Awaken the corresponding synchronize_rcu() instance now that a
175 * grace period has elapsed.
177 static void wakeme_after_rcu(struct rcu_head
*head
)
179 struct rcu_synchronize
*rcu
;
181 rcu
= container_of(head
, struct rcu_synchronize
, head
);
182 complete(&rcu
->completion
);
185 void wait_rcu_gp(call_rcu_func_t crf
)
187 struct rcu_synchronize rcu
;
189 init_rcu_head_on_stack(&rcu
.head
);
190 init_completion(&rcu
.completion
);
191 /* Will wake me after RCU finished. */
192 crf(&rcu
.head
, wakeme_after_rcu
);
194 wait_for_completion(&rcu
.completion
);
195 destroy_rcu_head_on_stack(&rcu
.head
);
197 EXPORT_SYMBOL_GPL(wait_rcu_gp
);
199 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
200 void init_rcu_head(struct rcu_head
*head
)
202 debug_object_init(head
, &rcuhead_debug_descr
);
205 void destroy_rcu_head(struct rcu_head
*head
)
207 debug_object_free(head
, &rcuhead_debug_descr
);
211 * fixup_activate is called when:
212 * - an active object is activated
213 * - an unknown object is activated (might be a statically initialized object)
214 * Activation is performed internally by call_rcu().
216 static int rcuhead_fixup_activate(void *addr
, enum debug_obj_state state
)
218 struct rcu_head
*head
= addr
;
222 case ODEBUG_STATE_NOTAVAILABLE
:
224 * This is not really a fixup. We just make sure that it is
225 * tracked in the object tracker.
227 debug_object_init(head
, &rcuhead_debug_descr
);
228 debug_object_activate(head
, &rcuhead_debug_descr
);
236 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
237 * @head: pointer to rcu_head structure to be initialized
239 * This function informs debugobjects of a new rcu_head structure that
240 * has been allocated as an auto variable on the stack. This function
241 * is not required for rcu_head structures that are statically defined or
242 * that are dynamically allocated on the heap. This function has no
243 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
245 void init_rcu_head_on_stack(struct rcu_head
*head
)
247 debug_object_init_on_stack(head
, &rcuhead_debug_descr
);
249 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack
);
252 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
253 * @head: pointer to rcu_head structure to be initialized
255 * This function informs debugobjects that an on-stack rcu_head structure
256 * is about to go out of scope. As with init_rcu_head_on_stack(), this
257 * function is not required for rcu_head structures that are statically
258 * defined or that are dynamically allocated on the heap. Also as with
259 * init_rcu_head_on_stack(), this function has no effect for
260 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
262 void destroy_rcu_head_on_stack(struct rcu_head
*head
)
264 debug_object_free(head
, &rcuhead_debug_descr
);
266 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack
);
268 struct debug_obj_descr rcuhead_debug_descr
= {
270 .fixup_activate
= rcuhead_fixup_activate
,
272 EXPORT_SYMBOL_GPL(rcuhead_debug_descr
);
273 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
275 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
276 void do_trace_rcu_torture_read(const char *rcutorturename
, struct rcu_head
*rhp
,
278 unsigned long c_old
, unsigned long c
)
280 trace_rcu_torture_read(rcutorturename
, rhp
, secs
, c_old
, c
);
282 EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read
);
284 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
288 #ifdef CONFIG_RCU_STALL_COMMON
290 #ifdef CONFIG_PROVE_RCU
291 #define RCU_STALL_DELAY_DELTA (5 * HZ)
293 #define RCU_STALL_DELAY_DELTA 0
296 int rcu_cpu_stall_suppress __read_mostly
; /* 1 = suppress stall warnings. */
297 static int rcu_cpu_stall_timeout __read_mostly
= CONFIG_RCU_CPU_STALL_TIMEOUT
;
299 module_param(rcu_cpu_stall_suppress
, int, 0644);
300 module_param(rcu_cpu_stall_timeout
, int, 0644);
302 int rcu_jiffies_till_stall_check(void)
304 int till_stall_check
= ACCESS_ONCE(rcu_cpu_stall_timeout
);
307 * Limit check must be consistent with the Kconfig limits
308 * for CONFIG_RCU_CPU_STALL_TIMEOUT.
310 if (till_stall_check
< 3) {
311 ACCESS_ONCE(rcu_cpu_stall_timeout
) = 3;
312 till_stall_check
= 3;
313 } else if (till_stall_check
> 300) {
314 ACCESS_ONCE(rcu_cpu_stall_timeout
) = 300;
315 till_stall_check
= 300;
317 return till_stall_check
* HZ
+ RCU_STALL_DELAY_DELTA
;
320 void rcu_sysrq_start(void)
322 if (!rcu_cpu_stall_suppress
)
323 rcu_cpu_stall_suppress
= 2;
326 void rcu_sysrq_end(void)
328 if (rcu_cpu_stall_suppress
== 2)
329 rcu_cpu_stall_suppress
= 0;
332 static int rcu_panic(struct notifier_block
*this, unsigned long ev
, void *ptr
)
334 rcu_cpu_stall_suppress
= 1;
338 static struct notifier_block rcu_panic_block
= {
339 .notifier_call
= rcu_panic
,
342 static int __init
check_cpu_stall_init(void)
344 atomic_notifier_chain_register(&panic_notifier_list
, &rcu_panic_block
);
347 early_initcall(check_cpu_stall_init
);
349 #endif /* #ifdef CONFIG_RCU_STALL_COMMON */