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, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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
52 #include <trace/events/rcu.h>
56 MODULE_ALIAS("rcupdate");
57 #ifdef MODULE_PARAM_PREFIX
58 #undef MODULE_PARAM_PREFIX
60 #define MODULE_PARAM_PREFIX "rcupdate."
62 module_param(rcu_expedited
, int, 0);
64 #ifdef CONFIG_PREEMPT_RCU
67 * Preemptible RCU implementation for rcu_read_lock().
68 * Just increment ->rcu_read_lock_nesting, shared state will be updated
71 void __rcu_read_lock(void)
73 current
->rcu_read_lock_nesting
++;
74 barrier(); /* critical section after entry code. */
76 EXPORT_SYMBOL_GPL(__rcu_read_lock
);
79 * Preemptible RCU implementation for rcu_read_unlock().
80 * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
81 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
82 * invoke rcu_read_unlock_special() to clean up after a context switch
83 * in an RCU read-side critical section and other special cases.
85 void __rcu_read_unlock(void)
87 struct task_struct
*t
= current
;
89 if (t
->rcu_read_lock_nesting
!= 1) {
90 --t
->rcu_read_lock_nesting
;
92 barrier(); /* critical section before exit code. */
93 t
->rcu_read_lock_nesting
= INT_MIN
;
94 #ifdef CONFIG_PROVE_RCU_DELAY
95 udelay(10); /* Make preemption more probable. */
96 #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
97 barrier(); /* assign before ->rcu_read_unlock_special load */
98 if (unlikely(ACCESS_ONCE(t
->rcu_read_unlock_special
)))
99 rcu_read_unlock_special(t
);
100 barrier(); /* ->rcu_read_unlock_special load before assign */
101 t
->rcu_read_lock_nesting
= 0;
103 #ifdef CONFIG_PROVE_LOCKING
105 int rrln
= ACCESS_ONCE(t
->rcu_read_lock_nesting
);
107 WARN_ON_ONCE(rrln
< 0 && rrln
> INT_MIN
/ 2);
109 #endif /* #ifdef CONFIG_PROVE_LOCKING */
111 EXPORT_SYMBOL_GPL(__rcu_read_unlock
);
113 #endif /* #ifdef CONFIG_PREEMPT_RCU */
115 #ifdef CONFIG_DEBUG_LOCK_ALLOC
116 static struct lock_class_key rcu_lock_key
;
117 struct lockdep_map rcu_lock_map
=
118 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key
);
119 EXPORT_SYMBOL_GPL(rcu_lock_map
);
121 static struct lock_class_key rcu_bh_lock_key
;
122 struct lockdep_map rcu_bh_lock_map
=
123 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key
);
124 EXPORT_SYMBOL_GPL(rcu_bh_lock_map
);
126 static struct lock_class_key rcu_sched_lock_key
;
127 struct lockdep_map rcu_sched_lock_map
=
128 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key
);
129 EXPORT_SYMBOL_GPL(rcu_sched_lock_map
);
131 int notrace
debug_lockdep_rcu_enabled(void)
133 return rcu_scheduler_active
&& debug_locks
&&
134 current
->lockdep_recursion
== 0;
136 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled
);
139 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
141 * Check for bottom half being disabled, which covers both the
142 * CONFIG_PROVE_RCU and not cases. Note that if someone uses
143 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
144 * will show the situation. This is useful for debug checks in functions
145 * that require that they be called within an RCU read-side critical
148 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
150 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
151 * offline from an RCU perspective, so check for those as well.
153 int rcu_read_lock_bh_held(void)
155 if (!debug_lockdep_rcu_enabled())
157 if (!rcu_is_watching())
159 if (!rcu_lockdep_current_cpu_online())
161 return in_softirq() || irqs_disabled();
163 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held
);
165 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
167 struct rcu_synchronize
{
168 struct rcu_head head
;
169 struct completion completion
;
173 * Awaken the corresponding synchronize_rcu() instance now that a
174 * grace period has elapsed.
176 static void wakeme_after_rcu(struct rcu_head
*head
)
178 struct rcu_synchronize
*rcu
;
180 rcu
= container_of(head
, struct rcu_synchronize
, head
);
181 complete(&rcu
->completion
);
184 void wait_rcu_gp(call_rcu_func_t crf
)
186 struct rcu_synchronize rcu
;
188 init_rcu_head_on_stack(&rcu
.head
);
189 init_completion(&rcu
.completion
);
190 /* Will wake me after RCU finished. */
191 crf(&rcu
.head
, wakeme_after_rcu
);
193 wait_for_completion(&rcu
.completion
);
194 destroy_rcu_head_on_stack(&rcu
.head
);
196 EXPORT_SYMBOL_GPL(wait_rcu_gp
);
198 #ifdef CONFIG_PROVE_RCU
200 * wrapper function to avoid #include problems.
202 int rcu_my_thread_group_empty(void)
204 return thread_group_empty(current
);
206 EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty
);
207 #endif /* #ifdef CONFIG_PROVE_RCU */
209 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
210 static inline void debug_init_rcu_head(struct rcu_head
*head
)
212 debug_object_init(head
, &rcuhead_debug_descr
);
215 static inline void debug_rcu_head_free(struct rcu_head
*head
)
217 debug_object_free(head
, &rcuhead_debug_descr
);
221 * fixup_activate is called when:
222 * - an active object is activated
223 * - an unknown object is activated (might be a statically initialized object)
224 * Activation is performed internally by call_rcu().
226 static int rcuhead_fixup_activate(void *addr
, enum debug_obj_state state
)
228 struct rcu_head
*head
= addr
;
232 case ODEBUG_STATE_NOTAVAILABLE
:
234 * This is not really a fixup. We just make sure that it is
235 * tracked in the object tracker.
237 debug_object_init(head
, &rcuhead_debug_descr
);
238 debug_object_activate(head
, &rcuhead_debug_descr
);
246 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
247 * @head: pointer to rcu_head structure to be initialized
249 * This function informs debugobjects of a new rcu_head structure that
250 * has been allocated as an auto variable on the stack. This function
251 * is not required for rcu_head structures that are statically defined or
252 * that are dynamically allocated on the heap. This function has no
253 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
255 void init_rcu_head_on_stack(struct rcu_head
*head
)
257 debug_object_init_on_stack(head
, &rcuhead_debug_descr
);
259 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack
);
262 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
263 * @head: pointer to rcu_head structure to be initialized
265 * This function informs debugobjects that an on-stack rcu_head structure
266 * is about to go out of scope. As with init_rcu_head_on_stack(), this
267 * function is not required for rcu_head structures that are statically
268 * defined or that are dynamically allocated on the heap. Also as with
269 * init_rcu_head_on_stack(), this function has no effect for
270 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
272 void destroy_rcu_head_on_stack(struct rcu_head
*head
)
274 debug_object_free(head
, &rcuhead_debug_descr
);
276 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack
);
278 struct debug_obj_descr rcuhead_debug_descr
= {
280 .fixup_activate
= rcuhead_fixup_activate
,
282 EXPORT_SYMBOL_GPL(rcuhead_debug_descr
);
283 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
285 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
286 void do_trace_rcu_torture_read(const char *rcutorturename
, struct rcu_head
*rhp
,
288 unsigned long c_old
, unsigned long c
)
290 trace_rcu_torture_read(rcutorturename
, rhp
, secs
, c_old
, c
);
292 EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read
);
294 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
298 #ifdef CONFIG_RCU_STALL_COMMON
300 #ifdef CONFIG_PROVE_RCU
301 #define RCU_STALL_DELAY_DELTA (5 * HZ)
303 #define RCU_STALL_DELAY_DELTA 0
306 int rcu_cpu_stall_suppress __read_mostly
; /* 1 = suppress stall warnings. */
307 static int rcu_cpu_stall_timeout __read_mostly
= CONFIG_RCU_CPU_STALL_TIMEOUT
;
309 module_param(rcu_cpu_stall_suppress
, int, 0644);
310 module_param(rcu_cpu_stall_timeout
, int, 0644);
312 int rcu_jiffies_till_stall_check(void)
314 int till_stall_check
= ACCESS_ONCE(rcu_cpu_stall_timeout
);
317 * Limit check must be consistent with the Kconfig limits
318 * for CONFIG_RCU_CPU_STALL_TIMEOUT.
320 if (till_stall_check
< 3) {
321 ACCESS_ONCE(rcu_cpu_stall_timeout
) = 3;
322 till_stall_check
= 3;
323 } else if (till_stall_check
> 300) {
324 ACCESS_ONCE(rcu_cpu_stall_timeout
) = 300;
325 till_stall_check
= 300;
327 return till_stall_check
* HZ
+ RCU_STALL_DELAY_DELTA
;
330 static int rcu_panic(struct notifier_block
*this, unsigned long ev
, void *ptr
)
332 rcu_cpu_stall_suppress
= 1;
336 static struct notifier_block rcu_panic_block
= {
337 .notifier_call
= rcu_panic
,
340 static int __init
check_cpu_stall_init(void)
342 atomic_notifier_chain_register(&panic_notifier_list
, &rcu_panic_block
);
345 early_initcall(check_cpu_stall_init
);
347 #endif /* #ifdef CONFIG_RCU_STALL_COMMON */