rcu: Merge preemptable-RCU functionality into hierarchical RCU
[linux-2.6.git] / kernel / rcutree_plugin.h
1 /*
2  * Read-Copy Update mechanism for mutual exclusion (tree-based version)
3  * Internal non-public definitions that provide either classic
4  * or preemptable semantics.
5  *
6  * This program is free software; you can redistribute it and/or modify
7  * it under the terms of the GNU General Public License as published by
8  * the Free Software Foundation; either version 2 of the License, or
9  * (at your option) any later version.
10  *
11  * This program is distributed in the hope that it will be useful,
12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14  * GNU General Public License for more details.
15  *
16  * You should have received a copy of the GNU General Public License
17  * along with this program; if not, write to the Free Software
18  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
19  *
20  * Copyright Red Hat, 2009
21  * Copyright IBM Corporation, 2009
22  *
23  * Author: Ingo Molnar <mingo@elte.hu>
24  *         Paul E. McKenney <paulmck@linux.vnet.ibm.com>
25  */
26
27
28 #ifdef CONFIG_TREE_PREEMPT_RCU
29
30 struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state);
31 DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
32
33 /*
34  * Tell them what RCU they are running.
35  */
36 static inline void rcu_bootup_announce(void)
37 {
38         printk(KERN_INFO
39                "Experimental preemptable hierarchical RCU implementation.\n");
40 }
41
42 /*
43  * Return the number of RCU-preempt batches processed thus far
44  * for debug and statistics.
45  */
46 long rcu_batches_completed_preempt(void)
47 {
48         return rcu_preempt_state.completed;
49 }
50 EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
51
52 /*
53  * Return the number of RCU batches processed thus far for debug & stats.
54  */
55 long rcu_batches_completed(void)
56 {
57         return rcu_batches_completed_preempt();
58 }
59 EXPORT_SYMBOL_GPL(rcu_batches_completed);
60
61 /*
62  * Record a preemptable-RCU quiescent state for the specified CPU.  Note
63  * that this just means that the task currently running on the CPU is
64  * not in a quiescent state.  There might be any number of tasks blocked
65  * while in an RCU read-side critical section.
66  */
67 static void rcu_preempt_qs_record(int cpu)
68 {
69         struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
70         rdp->passed_quiesc = 1;
71         rdp->passed_quiesc_completed = rdp->completed;
72 }
73
74 /*
75  * We have entered the scheduler or are between softirqs in ksoftirqd.
76  * If we are in an RCU read-side critical section, we need to reflect
77  * that in the state of the rcu_node structure corresponding to this CPU.
78  * Caller must disable hardirqs.
79  */
80 static void rcu_preempt_qs(int cpu)
81 {
82         struct task_struct *t = current;
83         int phase;
84         struct rcu_data *rdp;
85         struct rcu_node *rnp;
86
87         if (t->rcu_read_lock_nesting &&
88             (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
89
90                 /* Possibly blocking in an RCU read-side critical section. */
91                 rdp = rcu_preempt_state.rda[cpu];
92                 rnp = rdp->mynode;
93                 spin_lock(&rnp->lock);
94                 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
95                 t->rcu_blocked_cpu = cpu;
96
97                 /*
98                  * If this CPU has already checked in, then this task
99                  * will hold up the next grace period rather than the
100                  * current grace period.  Queue the task accordingly.
101                  * If the task is queued for the current grace period
102                  * (i.e., this CPU has not yet passed through a quiescent
103                  * state for the current grace period), then as long
104                  * as that task remains queued, the current grace period
105                  * cannot end.
106                  */
107                 phase = !(rnp->qsmask & rdp->grpmask) ^ (rnp->gpnum & 0x1);
108                 list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]);
109                 smp_mb();  /* Ensure later ctxt swtch seen after above. */
110                 spin_unlock(&rnp->lock);
111         }
112
113         /*
114          * Either we were not in an RCU read-side critical section to
115          * begin with, or we have now recorded that critical section
116          * globally.  Either way, we can now note a quiescent state
117          * for this CPU.  Again, if we were in an RCU read-side critical
118          * section, and if that critical section was blocking the current
119          * grace period, then the fact that the task has been enqueued
120          * means that we continue to block the current grace period.
121          */
122         rcu_preempt_qs_record(cpu);
123         t->rcu_read_unlock_special &= ~(RCU_READ_UNLOCK_NEED_QS |
124                                         RCU_READ_UNLOCK_GOT_QS);
125 }
126
127 /*
128  * Tree-preemptable RCU implementation for rcu_read_lock().
129  * Just increment ->rcu_read_lock_nesting, shared state will be updated
130  * if we block.
131  */
132 void __rcu_read_lock(void)
133 {
134         ACCESS_ONCE(current->rcu_read_lock_nesting)++;
135         barrier();  /* needed if we ever invoke rcu_read_lock in rcutree.c */
136 }
137 EXPORT_SYMBOL_GPL(__rcu_read_lock);
138
139 static void rcu_read_unlock_special(struct task_struct *t)
140 {
141         int empty;
142         unsigned long flags;
143         unsigned long mask;
144         struct rcu_node *rnp;
145         int special;
146
147         /* NMI handlers cannot block and cannot safely manipulate state. */
148         if (in_nmi())
149                 return;
150
151         local_irq_save(flags);
152
153         /*
154          * If RCU core is waiting for this CPU to exit critical section,
155          * let it know that we have done so.
156          */
157         special = t->rcu_read_unlock_special;
158         if (special & RCU_READ_UNLOCK_NEED_QS) {
159                 t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
160                 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_GOT_QS;
161         }
162
163         /* Hardware IRQ handlers cannot block. */
164         if (in_irq()) {
165                 local_irq_restore(flags);
166                 return;
167         }
168
169         /* Clean up if blocked during RCU read-side critical section. */
170         if (special & RCU_READ_UNLOCK_BLOCKED) {
171                 t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
172
173                 /* Remove this task from the list it blocked on. */
174                 rnp = rcu_preempt_state.rda[t->rcu_blocked_cpu]->mynode;
175                 spin_lock(&rnp->lock);
176                 empty = list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]);
177                 list_del_init(&t->rcu_node_entry);
178                 t->rcu_blocked_cpu = -1;
179
180                 /*
181                  * If this was the last task on the current list, and if
182                  * we aren't waiting on any CPUs, report the quiescent state.
183                  * Note that both cpu_quiet_msk_finish() and cpu_quiet_msk()
184                  * drop rnp->lock and restore irq.
185                  */
186                 if (!empty && rnp->qsmask == 0 &&
187                     list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1])) {
188                         t->rcu_read_unlock_special &=
189                                 ~(RCU_READ_UNLOCK_NEED_QS |
190                                   RCU_READ_UNLOCK_GOT_QS);
191                         if (rnp->parent == NULL) {
192                                 /* Only one rcu_node in the tree. */
193                                 cpu_quiet_msk_finish(&rcu_preempt_state, flags);
194                                 return;
195                         }
196                         /* Report up the rest of the hierarchy. */
197                         mask = rnp->grpmask;
198                         spin_unlock_irqrestore(&rnp->lock, flags);
199                         rnp = rnp->parent;
200                         spin_lock_irqsave(&rnp->lock, flags);
201                         cpu_quiet_msk(mask, &rcu_preempt_state, rnp, flags);
202                         return;
203                 }
204                 spin_unlock(&rnp->lock);
205         }
206         local_irq_restore(flags);
207 }
208
209 /*
210  * Tree-preemptable RCU implementation for rcu_read_unlock().
211  * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
212  * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
213  * invoke rcu_read_unlock_special() to clean up after a context switch
214  * in an RCU read-side critical section and other special cases.
215  */
216 void __rcu_read_unlock(void)
217 {
218         struct task_struct *t = current;
219
220         barrier();  /* needed if we ever invoke rcu_read_unlock in rcutree.c */
221         if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 &&
222             unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
223                 rcu_read_unlock_special(t);
224 }
225 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
226
227 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
228
229 /*
230  * Scan the current list of tasks blocked within RCU read-side critical
231  * sections, printing out the tid of each.
232  */
233 static void rcu_print_task_stall(struct rcu_node *rnp)
234 {
235         unsigned long flags;
236         struct list_head *lp;
237         int phase = rnp->gpnum & 0x1;
238         struct task_struct *t;
239
240         if (!list_empty(&rnp->blocked_tasks[phase])) {
241                 spin_lock_irqsave(&rnp->lock, flags);
242                 phase = rnp->gpnum & 0x1; /* re-read under lock. */
243                 lp = &rnp->blocked_tasks[phase];
244                 list_for_each_entry(t, lp, rcu_node_entry)
245                         printk(" P%d", t->pid);
246                 spin_unlock_irqrestore(&rnp->lock, flags);
247         }
248 }
249
250 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
251
252 /*
253  * Check for preempted RCU readers for the specified rcu_node structure.
254  * If the caller needs a reliable answer, it must hold the rcu_node's
255  * >lock.
256  */
257 static int rcu_preempted_readers(struct rcu_node *rnp)
258 {
259         return !list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]);
260 }
261
262 /*
263  * Check for a quiescent state from the current CPU.  When a task blocks,
264  * the task is recorded in the corresponding CPU's rcu_node structure,
265  * which is checked elsewhere.
266  *
267  * Caller must disable hard irqs.
268  */
269 static void rcu_preempt_check_callbacks(int cpu)
270 {
271         struct task_struct *t = current;
272
273         if (t->rcu_read_lock_nesting == 0) {
274                 t->rcu_read_unlock_special &=
275                         ~(RCU_READ_UNLOCK_NEED_QS | RCU_READ_UNLOCK_GOT_QS);
276                 rcu_preempt_qs_record(cpu);
277                 return;
278         }
279         if (per_cpu(rcu_preempt_data, cpu).qs_pending) {
280                 if (t->rcu_read_unlock_special & RCU_READ_UNLOCK_GOT_QS) {
281                         rcu_preempt_qs_record(cpu);
282                         t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_GOT_QS;
283                 } else if (!(t->rcu_read_unlock_special &
284                              RCU_READ_UNLOCK_NEED_QS)) {
285                         t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
286                 }
287         }
288 }
289
290 /*
291  * Process callbacks for preemptable RCU.
292  */
293 static void rcu_preempt_process_callbacks(void)
294 {
295         __rcu_process_callbacks(&rcu_preempt_state,
296                                 &__get_cpu_var(rcu_preempt_data));
297 }
298
299 /*
300  * Queue a preemptable-RCU callback for invocation after a grace period.
301  */
302 void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
303 {
304         __call_rcu(head, func, &rcu_preempt_state);
305 }
306 EXPORT_SYMBOL_GPL(call_rcu);
307
308 /*
309  * Check to see if there is any immediate preemptable-RCU-related work
310  * to be done.
311  */
312 static int rcu_preempt_pending(int cpu)
313 {
314         return __rcu_pending(&rcu_preempt_state,
315                              &per_cpu(rcu_preempt_data, cpu));
316 }
317
318 /*
319  * Does preemptable RCU need the CPU to stay out of dynticks mode?
320  */
321 static int rcu_preempt_needs_cpu(int cpu)
322 {
323         return !!per_cpu(rcu_preempt_data, cpu).nxtlist;
324 }
325
326 /*
327  * Initialize preemptable RCU's per-CPU data.
328  */
329 static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
330 {
331         rcu_init_percpu_data(cpu, &rcu_preempt_state, 1);
332 }
333
334 /*
335  * Check for a task exiting while in a preemptable-RCU read-side
336  * critical section, clean up if so.  No need to issue warnings,
337  * as debug_check_no_locks_held() already does this if lockdep
338  * is enabled.
339  */
340 void exit_rcu(void)
341 {
342         struct task_struct *t = current;
343
344         if (t->rcu_read_lock_nesting == 0)
345                 return;
346         t->rcu_read_lock_nesting = 1;
347         rcu_read_unlock();
348 }
349
350 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
351
352 /*
353  * Tell them what RCU they are running.
354  */
355 static inline void rcu_bootup_announce(void)
356 {
357         printk(KERN_INFO "Hierarchical RCU implementation.\n");
358 }
359
360 /*
361  * Return the number of RCU batches processed thus far for debug & stats.
362  */
363 long rcu_batches_completed(void)
364 {
365         return rcu_batches_completed_sched();
366 }
367 EXPORT_SYMBOL_GPL(rcu_batches_completed);
368
369 /*
370  * Because preemptable RCU does not exist, we never have to check for
371  * CPUs being in quiescent states.
372  */
373 static void rcu_preempt_qs(int cpu)
374 {
375 }
376
377 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
378
379 /*
380  * Because preemptable RCU does not exist, we never have to check for
381  * tasks blocked within RCU read-side critical sections.
382  */
383 static void rcu_print_task_stall(struct rcu_node *rnp)
384 {
385 }
386
387 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
388
389 /*
390  * Because preemptable RCU does not exist, there are never any preempted
391  * RCU readers.
392  */
393 static int rcu_preempted_readers(struct rcu_node *rnp)
394 {
395         return 0;
396 }
397
398 /*
399  * Because preemptable RCU does not exist, it never has any callbacks
400  * to check.
401  */
402 void rcu_preempt_check_callbacks(int cpu)
403 {
404 }
405
406 /*
407  * Because preemptable RCU does not exist, it never has any callbacks
408  * to process.
409  */
410 void rcu_preempt_process_callbacks(void)
411 {
412 }
413
414 /*
415  * In classic RCU, call_rcu() is just call_rcu_sched().
416  */
417 void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
418 {
419         call_rcu_sched(head, func);
420 }
421 EXPORT_SYMBOL_GPL(call_rcu);
422
423 /*
424  * Because preemptable RCU does not exist, it never has any work to do.
425  */
426 static int rcu_preempt_pending(int cpu)
427 {
428         return 0;
429 }
430
431 /*
432  * Because preemptable RCU does not exist, it never needs any CPU.
433  */
434 static int rcu_preempt_needs_cpu(int cpu)
435 {
436         return 0;
437 }
438
439 /*
440  * Because preemptable RCU does not exist, there is no per-CPU
441  * data to initialize.
442  */
443 static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
444 {
445 }
446
447 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */