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Linux/kernel/rcupdate.c

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  1 /*
  2  * Read-Copy Update mechanism for mutual exclusion
  3  *
  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.
  8  *
  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.
 13  *
 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.
 17  *
 18  * Copyright IBM Corporation, 2001
 19  *
 20  * Authors: Dipankar Sarma <dipankar@in.ibm.com>
 21  *          Manfred Spraul <manfred@colorfullife.com>
 22  *
 23  * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
 24  * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
 25  * Papers:
 26  * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
 27  * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
 28  *
 29  * For detailed explanation of Read-Copy Update mechanism see -
 30  *              http://lse.sourceforge.net/locking/rcupdate.html
 31  *
 32  */
 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 
 49 #define CREATE_TRACE_POINTS
 50 #include <trace/events/rcu.h>
 51 
 52 #include "rcu.h"
 53 
 54 #ifdef CONFIG_PREEMPT_RCU
 55 
 56 /*
 57  * Check for a task exiting while in a preemptible-RCU read-side
 58  * critical section, clean up if so.  No need to issue warnings,
 59  * as debug_check_no_locks_held() already does this if lockdep
 60  * is enabled.
 61  */
 62 void exit_rcu(void)
 63 {
 64         struct task_struct *t = current;
 65 
 66         if (likely(list_empty(&current->rcu_node_entry)))
 67                 return;
 68         t->rcu_read_lock_nesting = 1;
 69         barrier();
 70         t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
 71         __rcu_read_unlock();
 72 }
 73 
 74 #else /* #ifdef CONFIG_PREEMPT_RCU */
 75 
 76 void exit_rcu(void)
 77 {
 78 }
 79 
 80 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 81 
 82 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 83 static struct lock_class_key rcu_lock_key;
 84 struct lockdep_map rcu_lock_map =
 85         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
 86 EXPORT_SYMBOL_GPL(rcu_lock_map);
 87 
 88 static struct lock_class_key rcu_bh_lock_key;
 89 struct lockdep_map rcu_bh_lock_map =
 90         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
 91 EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
 92 
 93 static struct lock_class_key rcu_sched_lock_key;
 94 struct lockdep_map rcu_sched_lock_map =
 95         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
 96 EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
 97 #endif
 98 
 99 #ifdef CONFIG_DEBUG_LOCK_ALLOC
100 
101 int debug_lockdep_rcu_enabled(void)
102 {
103         return rcu_scheduler_active && debug_locks &&
104                current->lockdep_recursion == 0;
105 }
106 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
107 
108 /**
109  * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
110  *
111  * Check for bottom half being disabled, which covers both the
112  * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
113  * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
114  * will show the situation.  This is useful for debug checks in functions
115  * that require that they be called within an RCU read-side critical
116  * section.
117  *
118  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
119  *
120  * Note that rcu_read_lock() is disallowed if the CPU is either idle or
121  * offline from an RCU perspective, so check for those as well.
122  */
123 int rcu_read_lock_bh_held(void)
124 {
125         if (!debug_lockdep_rcu_enabled())
126                 return 1;
127         if (rcu_is_cpu_idle())
128                 return 0;
129         if (!rcu_lockdep_current_cpu_online())
130                 return 0;
131         return in_softirq() || irqs_disabled();
132 }
133 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
134 
135 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
136 
137 struct rcu_synchronize {
138         struct rcu_head head;
139         struct completion completion;
140 };
141 
142 /*
143  * Awaken the corresponding synchronize_rcu() instance now that a
144  * grace period has elapsed.
145  */
146 static void wakeme_after_rcu(struct rcu_head  *head)
147 {
148         struct rcu_synchronize *rcu;
149 
150         rcu = container_of(head, struct rcu_synchronize, head);
151         complete(&rcu->completion);
152 }
153 
154 void wait_rcu_gp(call_rcu_func_t crf)
155 {
156         struct rcu_synchronize rcu;
157 
158         init_rcu_head_on_stack(&rcu.head);
159         init_completion(&rcu.completion);
160         /* Will wake me after RCU finished. */
161         crf(&rcu.head, wakeme_after_rcu);
162         /* Wait for it. */
163         wait_for_completion(&rcu.completion);
164         destroy_rcu_head_on_stack(&rcu.head);
165 }
166 EXPORT_SYMBOL_GPL(wait_rcu_gp);
167 
168 #ifdef CONFIG_PROVE_RCU
169 /*
170  * wrapper function to avoid #include problems.
171  */
172 int rcu_my_thread_group_empty(void)
173 {
174         return thread_group_empty(current);
175 }
176 EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
177 #endif /* #ifdef CONFIG_PROVE_RCU */
178 
179 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
180 static inline void debug_init_rcu_head(struct rcu_head *head)
181 {
182         debug_object_init(head, &rcuhead_debug_descr);
183 }
184 
185 static inline void debug_rcu_head_free(struct rcu_head *head)
186 {
187         debug_object_free(head, &rcuhead_debug_descr);
188 }
189 
190 /*
191  * fixup_init is called when:
192  * - an active object is initialized
193  */
194 static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
195 {
196         struct rcu_head *head = addr;
197 
198         switch (state) {
199         case ODEBUG_STATE_ACTIVE:
200                 /*
201                  * Ensure that queued callbacks are all executed.
202                  * If we detect that we are nested in a RCU read-side critical
203                  * section, we should simply fail, otherwise we would deadlock.
204                  * In !PREEMPT configurations, there is no way to tell if we are
205                  * in a RCU read-side critical section or not, so we never
206                  * attempt any fixup and just print a warning.
207                  */
208 #ifndef CONFIG_PREEMPT
209                 WARN_ON_ONCE(1);
210                 return 0;
211 #endif
212                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
213                     irqs_disabled()) {
214                         WARN_ON_ONCE(1);
215                         return 0;
216                 }
217                 rcu_barrier();
218                 rcu_barrier_sched();
219                 rcu_barrier_bh();
220                 debug_object_init(head, &rcuhead_debug_descr);
221                 return 1;
222         default:
223                 return 0;
224         }
225 }
226 
227 /*
228  * fixup_activate is called when:
229  * - an active object is activated
230  * - an unknown object is activated (might be a statically initialized object)
231  * Activation is performed internally by call_rcu().
232  */
233 static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
234 {
235         struct rcu_head *head = addr;
236 
237         switch (state) {
238 
239         case ODEBUG_STATE_NOTAVAILABLE:
240                 /*
241                  * This is not really a fixup. We just make sure that it is
242                  * tracked in the object tracker.
243                  */
244                 debug_object_init(head, &rcuhead_debug_descr);
245                 debug_object_activate(head, &rcuhead_debug_descr);
246                 return 0;
247 
248         case ODEBUG_STATE_ACTIVE:
249                 /*
250                  * Ensure that queued callbacks are all executed.
251                  * If we detect that we are nested in a RCU read-side critical
252                  * section, we should simply fail, otherwise we would deadlock.
253                  * In !PREEMPT configurations, there is no way to tell if we are
254                  * in a RCU read-side critical section or not, so we never
255                  * attempt any fixup and just print a warning.
256                  */
257 #ifndef CONFIG_PREEMPT
258                 WARN_ON_ONCE(1);
259                 return 0;
260 #endif
261                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
262                     irqs_disabled()) {
263                         WARN_ON_ONCE(1);
264                         return 0;
265                 }
266                 rcu_barrier();
267                 rcu_barrier_sched();
268                 rcu_barrier_bh();
269                 debug_object_activate(head, &rcuhead_debug_descr);
270                 return 1;
271         default:
272                 return 0;
273         }
274 }
275 
276 /*
277  * fixup_free is called when:
278  * - an active object is freed
279  */
280 static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
281 {
282         struct rcu_head *head = addr;
283 
284         switch (state) {
285         case ODEBUG_STATE_ACTIVE:
286                 /*
287                  * Ensure that queued callbacks are all executed.
288                  * If we detect that we are nested in a RCU read-side critical
289                  * section, we should simply fail, otherwise we would deadlock.
290                  * In !PREEMPT configurations, there is no way to tell if we are
291                  * in a RCU read-side critical section or not, so we never
292                  * attempt any fixup and just print a warning.
293                  */
294 #ifndef CONFIG_PREEMPT
295                 WARN_ON_ONCE(1);
296                 return 0;
297 #endif
298                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
299                     irqs_disabled()) {
300                         WARN_ON_ONCE(1);
301                         return 0;
302                 }
303                 rcu_barrier();
304                 rcu_barrier_sched();
305                 rcu_barrier_bh();
306                 debug_object_free(head, &rcuhead_debug_descr);
307                 return 1;
308         default:
309                 return 0;
310         }
311 }
312 
313 /**
314  * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
315  * @head: pointer to rcu_head structure to be initialized
316  *
317  * This function informs debugobjects of a new rcu_head structure that
318  * has been allocated as an auto variable on the stack.  This function
319  * is not required for rcu_head structures that are statically defined or
320  * that are dynamically allocated on the heap.  This function has no
321  * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
322  */
323 void init_rcu_head_on_stack(struct rcu_head *head)
324 {
325         debug_object_init_on_stack(head, &rcuhead_debug_descr);
326 }
327 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
328 
329 /**
330  * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
331  * @head: pointer to rcu_head structure to be initialized
332  *
333  * This function informs debugobjects that an on-stack rcu_head structure
334  * is about to go out of scope.  As with init_rcu_head_on_stack(), this
335  * function is not required for rcu_head structures that are statically
336  * defined or that are dynamically allocated on the heap.  Also as with
337  * init_rcu_head_on_stack(), this function has no effect for
338  * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
339  */
340 void destroy_rcu_head_on_stack(struct rcu_head *head)
341 {
342         debug_object_free(head, &rcuhead_debug_descr);
343 }
344 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
345 
346 struct debug_obj_descr rcuhead_debug_descr = {
347         .name = "rcu_head",
348         .fixup_init = rcuhead_fixup_init,
349         .fixup_activate = rcuhead_fixup_activate,
350         .fixup_free = rcuhead_fixup_free,
351 };
352 EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
353 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
354 
355 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
356 void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp)
357 {
358         trace_rcu_torture_read(rcutorturename, rhp);
359 }
360 EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
361 #else
362 #define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
363 #endif
364 

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