crypto: tegra-se: fix resourse leak
[linux-3.10.git] / kernel / rcutiny_plugin.h
1 /*
2  * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition
3  * Internal non-public definitions that provide either classic
4  * or preemptible 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 (c) 2010 Linaro
21  *
22  * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
23  */
24
25 #include <linux/kthread.h>
26 #include <linux/module.h>
27 #include <linux/debugfs.h>
28 #include <linux/seq_file.h>
29
30 /* Global control variables for rcupdate callback mechanism. */
31 struct rcu_ctrlblk {
32         struct rcu_head *rcucblist;     /* List of pending callbacks (CBs). */
33         struct rcu_head **donetail;     /* ->next pointer of last "done" CB. */
34         struct rcu_head **curtail;      /* ->next pointer of last CB. */
35         RCU_TRACE(long qlen);           /* Number of pending CBs. */
36         RCU_TRACE(unsigned long gp_start); /* Start time for stalls. */
37         RCU_TRACE(unsigned long ticks_this_gp); /* Statistic for stalls. */
38         RCU_TRACE(unsigned long jiffies_stall); /* Jiffies at next stall. */
39         RCU_TRACE(char *name);          /* Name of RCU type. */
40 };
41
42 /* Definition for rcupdate control block. */
43 static struct rcu_ctrlblk rcu_sched_ctrlblk = {
44         .donetail       = &rcu_sched_ctrlblk.rcucblist,
45         .curtail        = &rcu_sched_ctrlblk.rcucblist,
46         RCU_TRACE(.name = "rcu_sched")
47 };
48
49 static struct rcu_ctrlblk rcu_bh_ctrlblk = {
50         .donetail       = &rcu_bh_ctrlblk.rcucblist,
51         .curtail        = &rcu_bh_ctrlblk.rcucblist,
52         RCU_TRACE(.name = "rcu_bh")
53 };
54
55 #ifdef CONFIG_DEBUG_LOCK_ALLOC
56 int rcu_scheduler_active __read_mostly;
57 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
58 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
59
60 #ifdef CONFIG_RCU_TRACE
61
62 static void check_cpu_stall(struct rcu_ctrlblk *rcp)
63 {
64         unsigned long j;
65         unsigned long js;
66
67         if (rcu_cpu_stall_suppress)
68                 return;
69         rcp->ticks_this_gp++;
70         j = jiffies;
71         js = rcp->jiffies_stall;
72         if (*rcp->curtail && ULONG_CMP_GE(j, js)) {
73                 pr_err("INFO: %s stall on CPU (%lu ticks this GP) idle=%llx (t=%lu jiffies q=%ld)\n",
74                        rcp->name, rcp->ticks_this_gp, rcu_dynticks_nesting,
75                        jiffies - rcp->gp_start, rcp->qlen);
76                 dump_stack();
77         }
78         if (*rcp->curtail && ULONG_CMP_GE(j, js))
79                 rcp->jiffies_stall = jiffies +
80                         3 * rcu_jiffies_till_stall_check() + 3;
81         else if (ULONG_CMP_GE(j, js))
82                 rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
83 }
84
85 static void check_cpu_stall_preempt(void);
86
87 #endif /* #ifdef CONFIG_RCU_TRACE */
88
89 static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
90 {
91 #ifdef CONFIG_RCU_TRACE
92         rcp->ticks_this_gp = 0;
93         rcp->gp_start = jiffies;
94         rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
95 #endif /* #ifdef CONFIG_RCU_TRACE */
96 }
97
98 static void check_cpu_stalls(void)
99 {
100         RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
101         RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
102         RCU_TRACE(check_cpu_stall_preempt());
103 }
104
105 #ifdef CONFIG_TINY_PREEMPT_RCU
106
107 #include <linux/delay.h>
108
109 /* Global control variables for preemptible RCU. */
110 struct rcu_preempt_ctrlblk {
111         struct rcu_ctrlblk rcb; /* curtail: ->next ptr of last CB for GP. */
112         struct rcu_head **nexttail;
113                                 /* Tasks blocked in a preemptible RCU */
114                                 /*  read-side critical section while an */
115                                 /*  preemptible-RCU grace period is in */
116                                 /*  progress must wait for a later grace */
117                                 /*  period.  This pointer points to the */
118                                 /*  ->next pointer of the last task that */
119                                 /*  must wait for a later grace period, or */
120                                 /*  to &->rcb.rcucblist if there is no */
121                                 /*  such task. */
122         struct list_head blkd_tasks;
123                                 /* Tasks blocked in RCU read-side critical */
124                                 /*  section.  Tasks are placed at the head */
125                                 /*  of this list and age towards the tail. */
126         struct list_head *gp_tasks;
127                                 /* Pointer to the first task blocking the */
128                                 /*  current grace period, or NULL if there */
129                                 /*  is no such task. */
130         struct list_head *exp_tasks;
131                                 /* Pointer to first task blocking the */
132                                 /*  current expedited grace period, or NULL */
133                                 /*  if there is no such task.  If there */
134                                 /*  is no current expedited grace period, */
135                                 /*  then there cannot be any such task. */
136 #ifdef CONFIG_RCU_BOOST
137         struct list_head *boost_tasks;
138                                 /* Pointer to first task that needs to be */
139                                 /*  priority-boosted, or NULL if no priority */
140                                 /*  boosting is needed.  If there is no */
141                                 /*  current or expedited grace period, there */
142                                 /*  can be no such task. */
143 #endif /* #ifdef CONFIG_RCU_BOOST */
144         u8 gpnum;               /* Current grace period. */
145         u8 gpcpu;               /* Last grace period blocked by the CPU. */
146         u8 completed;           /* Last grace period completed. */
147                                 /*  If all three are equal, RCU is idle. */
148 #ifdef CONFIG_RCU_BOOST
149         unsigned long boost_time; /* When to start boosting (jiffies) */
150 #endif /* #ifdef CONFIG_RCU_BOOST */
151 #ifdef CONFIG_RCU_TRACE
152         unsigned long n_grace_periods;
153 #ifdef CONFIG_RCU_BOOST
154         unsigned long n_tasks_boosted;
155                                 /* Total number of tasks boosted. */
156         unsigned long n_exp_boosts;
157                                 /* Number of tasks boosted for expedited GP. */
158         unsigned long n_normal_boosts;
159                                 /* Number of tasks boosted for normal GP. */
160         unsigned long n_balk_blkd_tasks;
161                                 /* Refused to boost: no blocked tasks. */
162         unsigned long n_balk_exp_gp_tasks;
163                                 /* Refused to boost: nothing blocking GP. */
164         unsigned long n_balk_boost_tasks;
165                                 /* Refused to boost: already boosting. */
166         unsigned long n_balk_notyet;
167                                 /* Refused to boost: not yet time. */
168         unsigned long n_balk_nos;
169                                 /* Refused to boost: not sure why, though. */
170                                 /*  This can happen due to race conditions. */
171 #endif /* #ifdef CONFIG_RCU_BOOST */
172 #endif /* #ifdef CONFIG_RCU_TRACE */
173 };
174
175 static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = {
176         .rcb.donetail = &rcu_preempt_ctrlblk.rcb.rcucblist,
177         .rcb.curtail = &rcu_preempt_ctrlblk.rcb.rcucblist,
178         .nexttail = &rcu_preempt_ctrlblk.rcb.rcucblist,
179         .blkd_tasks = LIST_HEAD_INIT(rcu_preempt_ctrlblk.blkd_tasks),
180         RCU_TRACE(.rcb.name = "rcu_preempt")
181 };
182
183 static int rcu_preempted_readers_exp(void);
184 static void rcu_report_exp_done(void);
185
186 /*
187  * Return true if the CPU has not yet responded to the current grace period.
188  */
189 static int rcu_cpu_blocking_cur_gp(void)
190 {
191         return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum;
192 }
193
194 /*
195  * Check for a running RCU reader.  Because there is only one CPU,
196  * there can be but one running RCU reader at a time.  ;-)
197  *
198  * Returns zero if there are no running readers.  Returns a positive
199  * number if there is at least one reader within its RCU read-side
200  * critical section.  Returns a negative number if an outermost reader
201  * is in the midst of exiting from its RCU read-side critical section
202  *
203  * Returns zero if there are no running readers.  Returns a positive
204  * number if there is at least one reader within its RCU read-side
205  * critical section.  Returns a negative number if an outermost reader
206  * is in the midst of exiting from its RCU read-side critical section.
207  */
208 static int rcu_preempt_running_reader(void)
209 {
210         return current->rcu_read_lock_nesting;
211 }
212
213 /*
214  * Check for preempted RCU readers blocking any grace period.
215  * If the caller needs a reliable answer, it must disable hard irqs.
216  */
217 static int rcu_preempt_blocked_readers_any(void)
218 {
219         return !list_empty(&rcu_preempt_ctrlblk.blkd_tasks);
220 }
221
222 /*
223  * Check for preempted RCU readers blocking the current grace period.
224  * If the caller needs a reliable answer, it must disable hard irqs.
225  */
226 static int rcu_preempt_blocked_readers_cgp(void)
227 {
228         return rcu_preempt_ctrlblk.gp_tasks != NULL;
229 }
230
231 /*
232  * Return true if another preemptible-RCU grace period is needed.
233  */
234 static int rcu_preempt_needs_another_gp(void)
235 {
236         return *rcu_preempt_ctrlblk.rcb.curtail != NULL;
237 }
238
239 /*
240  * Return true if a preemptible-RCU grace period is in progress.
241  * The caller must disable hardirqs.
242  */
243 static int rcu_preempt_gp_in_progress(void)
244 {
245         return rcu_preempt_ctrlblk.completed != rcu_preempt_ctrlblk.gpnum;
246 }
247
248 /*
249  * Advance a ->blkd_tasks-list pointer to the next entry, instead
250  * returning NULL if at the end of the list.
251  */
252 static struct list_head *rcu_next_node_entry(struct task_struct *t)
253 {
254         struct list_head *np;
255
256         np = t->rcu_node_entry.next;
257         if (np == &rcu_preempt_ctrlblk.blkd_tasks)
258                 np = NULL;
259         return np;
260 }
261
262 #ifdef CONFIG_RCU_TRACE
263
264 #ifdef CONFIG_RCU_BOOST
265 static void rcu_initiate_boost_trace(void);
266 #endif /* #ifdef CONFIG_RCU_BOOST */
267
268 /*
269  * Dump additional statistice for TINY_PREEMPT_RCU.
270  */
271 static void show_tiny_preempt_stats(struct seq_file *m)
272 {
273         seq_printf(m, "rcu_preempt: qlen=%ld gp=%lu g%u/p%u/c%u tasks=%c%c%c\n",
274                    rcu_preempt_ctrlblk.rcb.qlen,
275                    rcu_preempt_ctrlblk.n_grace_periods,
276                    rcu_preempt_ctrlblk.gpnum,
277                    rcu_preempt_ctrlblk.gpcpu,
278                    rcu_preempt_ctrlblk.completed,
279                    "T."[list_empty(&rcu_preempt_ctrlblk.blkd_tasks)],
280                    "N."[!rcu_preempt_ctrlblk.gp_tasks],
281                    "E."[!rcu_preempt_ctrlblk.exp_tasks]);
282 #ifdef CONFIG_RCU_BOOST
283         seq_printf(m, "%sttb=%c ntb=%lu neb=%lu nnb=%lu j=%04x bt=%04x\n",
284                    "             ",
285                    "B."[!rcu_preempt_ctrlblk.boost_tasks],
286                    rcu_preempt_ctrlblk.n_tasks_boosted,
287                    rcu_preempt_ctrlblk.n_exp_boosts,
288                    rcu_preempt_ctrlblk.n_normal_boosts,
289                    (int)(jiffies & 0xffff),
290                    (int)(rcu_preempt_ctrlblk.boost_time & 0xffff));
291         seq_printf(m, "%s: nt=%lu egt=%lu bt=%lu ny=%lu nos=%lu\n",
292                    "             balk",
293                    rcu_preempt_ctrlblk.n_balk_blkd_tasks,
294                    rcu_preempt_ctrlblk.n_balk_exp_gp_tasks,
295                    rcu_preempt_ctrlblk.n_balk_boost_tasks,
296                    rcu_preempt_ctrlblk.n_balk_notyet,
297                    rcu_preempt_ctrlblk.n_balk_nos);
298 #endif /* #ifdef CONFIG_RCU_BOOST */
299 }
300
301 #endif /* #ifdef CONFIG_RCU_TRACE */
302
303 #ifdef CONFIG_RCU_BOOST
304
305 #include "rtmutex_common.h"
306
307 #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
308
309 /* Controls for rcu_kthread() kthread. */
310 static struct task_struct *rcu_kthread_task;
311 static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
312 static unsigned long have_rcu_kthread_work;
313
314 /*
315  * Carry out RCU priority boosting on the task indicated by ->boost_tasks,
316  * and advance ->boost_tasks to the next task in the ->blkd_tasks list.
317  */
318 static int rcu_boost(void)
319 {
320         unsigned long flags;
321         struct rt_mutex mtx;
322         struct task_struct *t;
323         struct list_head *tb;
324
325         if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
326             rcu_preempt_ctrlblk.exp_tasks == NULL)
327                 return 0;  /* Nothing to boost. */
328
329         local_irq_save(flags);
330
331         /*
332          * Recheck with irqs disabled: all tasks in need of boosting
333          * might exit their RCU read-side critical sections on their own
334          * if we are preempted just before disabling irqs.
335          */
336         if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
337             rcu_preempt_ctrlblk.exp_tasks == NULL) {
338                 local_irq_restore(flags);
339                 return 0;
340         }
341
342         /*
343          * Preferentially boost tasks blocking expedited grace periods.
344          * This cannot starve the normal grace periods because a second
345          * expedited grace period must boost all blocked tasks, including
346          * those blocking the pre-existing normal grace period.
347          */
348         if (rcu_preempt_ctrlblk.exp_tasks != NULL) {
349                 tb = rcu_preempt_ctrlblk.exp_tasks;
350                 RCU_TRACE(rcu_preempt_ctrlblk.n_exp_boosts++);
351         } else {
352                 tb = rcu_preempt_ctrlblk.boost_tasks;
353                 RCU_TRACE(rcu_preempt_ctrlblk.n_normal_boosts++);
354         }
355         RCU_TRACE(rcu_preempt_ctrlblk.n_tasks_boosted++);
356
357         /*
358          * We boost task t by manufacturing an rt_mutex that appears to
359          * be held by task t.  We leave a pointer to that rt_mutex where
360          * task t can find it, and task t will release the mutex when it
361          * exits its outermost RCU read-side critical section.  Then
362          * simply acquiring this artificial rt_mutex will boost task
363          * t's priority.  (Thanks to tglx for suggesting this approach!)
364          */
365         t = container_of(tb, struct task_struct, rcu_node_entry);
366         rt_mutex_init_proxy_locked(&mtx, t);
367         t->rcu_boost_mutex = &mtx;
368         local_irq_restore(flags);
369         rt_mutex_lock(&mtx);
370         rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */
371
372         return ACCESS_ONCE(rcu_preempt_ctrlblk.boost_tasks) != NULL ||
373                ACCESS_ONCE(rcu_preempt_ctrlblk.exp_tasks) != NULL;
374 }
375
376 /*
377  * Check to see if it is now time to start boosting RCU readers blocking
378  * the current grace period, and, if so, tell the rcu_kthread_task to
379  * start boosting them.  If there is an expedited boost in progress,
380  * we wait for it to complete.
381  *
382  * If there are no blocked readers blocking the current grace period,
383  * return 0 to let the caller know, otherwise return 1.  Note that this
384  * return value is independent of whether or not boosting was done.
385  */
386 static int rcu_initiate_boost(void)
387 {
388         if (!rcu_preempt_blocked_readers_cgp() &&
389             rcu_preempt_ctrlblk.exp_tasks == NULL) {
390                 RCU_TRACE(rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++);
391                 return 0;
392         }
393         if (rcu_preempt_ctrlblk.exp_tasks != NULL ||
394             (rcu_preempt_ctrlblk.gp_tasks != NULL &&
395              rcu_preempt_ctrlblk.boost_tasks == NULL &&
396              ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))) {
397                 if (rcu_preempt_ctrlblk.exp_tasks == NULL)
398                         rcu_preempt_ctrlblk.boost_tasks =
399                                 rcu_preempt_ctrlblk.gp_tasks;
400                 invoke_rcu_callbacks();
401         } else {
402                 RCU_TRACE(rcu_initiate_boost_trace());
403         }
404         return 1;
405 }
406
407 #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
408
409 /*
410  * Do priority-boost accounting for the start of a new grace period.
411  */
412 static void rcu_preempt_boost_start_gp(void)
413 {
414         rcu_preempt_ctrlblk.boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
415 }
416
417 #else /* #ifdef CONFIG_RCU_BOOST */
418
419 /*
420  * If there is no RCU priority boosting, we don't initiate boosting,
421  * but we do indicate whether there are blocked readers blocking the
422  * current grace period.
423  */
424 static int rcu_initiate_boost(void)
425 {
426         return rcu_preempt_blocked_readers_cgp();
427 }
428
429 /*
430  * If there is no RCU priority boosting, nothing to do at grace-period start.
431  */
432 static void rcu_preempt_boost_start_gp(void)
433 {
434 }
435
436 #endif /* else #ifdef CONFIG_RCU_BOOST */
437
438 /*
439  * Record a preemptible-RCU quiescent state for the specified CPU.  Note
440  * that this just means that the task currently running on the CPU is
441  * in a quiescent state.  There might be any number of tasks blocked
442  * while in an RCU read-side critical section.
443  *
444  * Unlike the other rcu_*_qs() functions, callers to this function
445  * must disable irqs in order to protect the assignment to
446  * ->rcu_read_unlock_special.
447  *
448  * Because this is a single-CPU implementation, the only way a grace
449  * period can end is if the CPU is in a quiescent state.  The reason is
450  * that a blocked preemptible-RCU reader can exit its critical section
451  * only if the CPU is running it at the time.  Therefore, when the
452  * last task blocking the current grace period exits its RCU read-side
453  * critical section, neither the CPU nor blocked tasks will be stopping
454  * the current grace period.  (In contrast, SMP implementations
455  * might have CPUs running in RCU read-side critical sections that
456  * block later grace periods -- but this is not possible given only
457  * one CPU.)
458  */
459 static void rcu_preempt_cpu_qs(void)
460 {
461         /* Record both CPU and task as having responded to current GP. */
462         rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum;
463         current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
464
465         /* If there is no GP then there is nothing more to do.  */
466         if (!rcu_preempt_gp_in_progress())
467                 return;
468         /*
469          * Check up on boosting.  If there are readers blocking the
470          * current grace period, leave.
471          */
472         if (rcu_initiate_boost())
473                 return;
474
475         /* Advance callbacks. */
476         rcu_preempt_ctrlblk.completed = rcu_preempt_ctrlblk.gpnum;
477         rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.rcb.curtail;
478         rcu_preempt_ctrlblk.rcb.curtail = rcu_preempt_ctrlblk.nexttail;
479
480         /* If there are no blocked readers, next GP is done instantly. */
481         if (!rcu_preempt_blocked_readers_any())
482                 rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.nexttail;
483
484         /* If there are done callbacks, cause them to be invoked. */
485         if (*rcu_preempt_ctrlblk.rcb.donetail != NULL)
486                 invoke_rcu_callbacks();
487 }
488
489 /*
490  * Start a new RCU grace period if warranted.  Hard irqs must be disabled.
491  */
492 static void rcu_preempt_start_gp(void)
493 {
494         if (!rcu_preempt_gp_in_progress() && rcu_preempt_needs_another_gp()) {
495
496                 /* Official start of GP. */
497                 rcu_preempt_ctrlblk.gpnum++;
498                 RCU_TRACE(rcu_preempt_ctrlblk.n_grace_periods++);
499                 reset_cpu_stall_ticks(&rcu_preempt_ctrlblk.rcb);
500
501                 /* Any blocked RCU readers block new GP. */
502                 if (rcu_preempt_blocked_readers_any())
503                         rcu_preempt_ctrlblk.gp_tasks =
504                                 rcu_preempt_ctrlblk.blkd_tasks.next;
505
506                 /* Set up for RCU priority boosting. */
507                 rcu_preempt_boost_start_gp();
508
509                 /* If there is no running reader, CPU is done with GP. */
510                 if (!rcu_preempt_running_reader())
511                         rcu_preempt_cpu_qs();
512         }
513 }
514
515 /*
516  * We have entered the scheduler, and the current task might soon be
517  * context-switched away from.  If this task is in an RCU read-side
518  * critical section, we will no longer be able to rely on the CPU to
519  * record that fact, so we enqueue the task on the blkd_tasks list.
520  * If the task started after the current grace period began, as recorded
521  * by ->gpcpu, we enqueue at the beginning of the list.  Otherwise
522  * before the element referenced by ->gp_tasks (or at the tail if
523  * ->gp_tasks is NULL) and point ->gp_tasks at the newly added element.
524  * The task will dequeue itself when it exits the outermost enclosing
525  * RCU read-side critical section.  Therefore, the current grace period
526  * cannot be permitted to complete until the ->gp_tasks pointer becomes
527  * NULL.
528  *
529  * Caller must disable preemption.
530  */
531 void rcu_preempt_note_context_switch(void)
532 {
533         struct task_struct *t = current;
534         unsigned long flags;
535
536         local_irq_save(flags); /* must exclude scheduler_tick(). */
537         if (rcu_preempt_running_reader() > 0 &&
538             (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
539
540                 /* Possibly blocking in an RCU read-side critical section. */
541                 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
542
543                 /*
544                  * If this CPU has already checked in, then this task
545                  * will hold up the next grace period rather than the
546                  * current grace period.  Queue the task accordingly.
547                  * If the task is queued for the current grace period
548                  * (i.e., this CPU has not yet passed through a quiescent
549                  * state for the current grace period), then as long
550                  * as that task remains queued, the current grace period
551                  * cannot end.
552                  */
553                 list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks);
554                 if (rcu_cpu_blocking_cur_gp())
555                         rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry;
556         } else if (rcu_preempt_running_reader() < 0 &&
557                    t->rcu_read_unlock_special) {
558                 /*
559                  * Complete exit from RCU read-side critical section on
560                  * behalf of preempted instance of __rcu_read_unlock().
561                  */
562                 rcu_read_unlock_special(t);
563         }
564
565         /*
566          * Either we were not in an RCU read-side critical section to
567          * begin with, or we have now recorded that critical section
568          * globally.  Either way, we can now note a quiescent state
569          * for this CPU.  Again, if we were in an RCU read-side critical
570          * section, and if that critical section was blocking the current
571          * grace period, then the fact that the task has been enqueued
572          * means that current grace period continues to be blocked.
573          */
574         rcu_preempt_cpu_qs();
575         local_irq_restore(flags);
576 }
577
578 /*
579  * Handle special cases during rcu_read_unlock(), such as needing to
580  * notify RCU core processing or task having blocked during the RCU
581  * read-side critical section.
582  */
583 void rcu_read_unlock_special(struct task_struct *t)
584 {
585         int empty;
586         int empty_exp;
587         unsigned long flags;
588         struct list_head *np;
589 #ifdef CONFIG_RCU_BOOST
590         struct rt_mutex *rbmp = NULL;
591 #endif /* #ifdef CONFIG_RCU_BOOST */
592         int special;
593
594         /*
595          * NMI handlers cannot block and cannot safely manipulate state.
596          * They therefore cannot possibly be special, so just leave.
597          */
598         if (in_nmi())
599                 return;
600
601         local_irq_save(flags);
602
603         /*
604          * If RCU core is waiting for this CPU to exit critical section,
605          * let it know that we have done so.
606          */
607         special = t->rcu_read_unlock_special;
608         if (special & RCU_READ_UNLOCK_NEED_QS)
609                 rcu_preempt_cpu_qs();
610
611         /* Hardware IRQ handlers cannot block. */
612         if (in_irq() || in_serving_softirq()) {
613                 local_irq_restore(flags);
614                 return;
615         }
616
617         /* Clean up if blocked during RCU read-side critical section. */
618         if (special & RCU_READ_UNLOCK_BLOCKED) {
619                 t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
620
621                 /*
622                  * Remove this task from the ->blkd_tasks list and adjust
623                  * any pointers that might have been referencing it.
624                  */
625                 empty = !rcu_preempt_blocked_readers_cgp();
626                 empty_exp = rcu_preempt_ctrlblk.exp_tasks == NULL;
627                 np = rcu_next_node_entry(t);
628                 list_del_init(&t->rcu_node_entry);
629                 if (&t->rcu_node_entry == rcu_preempt_ctrlblk.gp_tasks)
630                         rcu_preempt_ctrlblk.gp_tasks = np;
631                 if (&t->rcu_node_entry == rcu_preempt_ctrlblk.exp_tasks)
632                         rcu_preempt_ctrlblk.exp_tasks = np;
633 #ifdef CONFIG_RCU_BOOST
634                 if (&t->rcu_node_entry == rcu_preempt_ctrlblk.boost_tasks)
635                         rcu_preempt_ctrlblk.boost_tasks = np;
636 #endif /* #ifdef CONFIG_RCU_BOOST */
637
638                 /*
639                  * If this was the last task on the current list, and if
640                  * we aren't waiting on the CPU, report the quiescent state
641                  * and start a new grace period if needed.
642                  */
643                 if (!empty && !rcu_preempt_blocked_readers_cgp()) {
644                         rcu_preempt_cpu_qs();
645                         rcu_preempt_start_gp();
646                 }
647
648                 /*
649                  * If this was the last task on the expedited lists,
650                  * then we need wake up the waiting task.
651                  */
652                 if (!empty_exp && rcu_preempt_ctrlblk.exp_tasks == NULL)
653                         rcu_report_exp_done();
654         }
655 #ifdef CONFIG_RCU_BOOST
656         /* Unboost self if was boosted. */
657         if (t->rcu_boost_mutex != NULL) {
658                 rbmp = t->rcu_boost_mutex;
659                 t->rcu_boost_mutex = NULL;
660                 rt_mutex_unlock(rbmp);
661         }
662 #endif /* #ifdef CONFIG_RCU_BOOST */
663         local_irq_restore(flags);
664 }
665
666 /*
667  * Check for a quiescent state from the current CPU.  When a task blocks,
668  * the task is recorded in the rcu_preempt_ctrlblk structure, which is
669  * checked elsewhere.  This is called from the scheduling-clock interrupt.
670  *
671  * Caller must disable hard irqs.
672  */
673 static void rcu_preempt_check_callbacks(void)
674 {
675         struct task_struct *t = current;
676
677         if (rcu_preempt_gp_in_progress() &&
678             (!rcu_preempt_running_reader() ||
679              !rcu_cpu_blocking_cur_gp()))
680                 rcu_preempt_cpu_qs();
681         if (&rcu_preempt_ctrlblk.rcb.rcucblist !=
682             rcu_preempt_ctrlblk.rcb.donetail)
683                 invoke_rcu_callbacks();
684         if (rcu_preempt_gp_in_progress() &&
685             rcu_cpu_blocking_cur_gp() &&
686             rcu_preempt_running_reader() > 0)
687                 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
688 }
689
690 /*
691  * TINY_PREEMPT_RCU has an extra callback-list tail pointer to
692  * update, so this is invoked from rcu_process_callbacks() to
693  * handle that case.  Of course, it is invoked for all flavors of
694  * RCU, but RCU callbacks can appear only on one of the lists, and
695  * neither ->nexttail nor ->donetail can possibly be NULL, so there
696  * is no need for an explicit check.
697  */
698 static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
699 {
700         if (rcu_preempt_ctrlblk.nexttail == rcp->donetail)
701                 rcu_preempt_ctrlblk.nexttail = &rcp->rcucblist;
702 }
703
704 /*
705  * Process callbacks for preemptible RCU.
706  */
707 static void rcu_preempt_process_callbacks(void)
708 {
709         __rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb);
710 }
711
712 /*
713  * Queue a preemptible -RCU callback for invocation after a grace period.
714  */
715 void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
716 {
717         unsigned long flags;
718
719         debug_rcu_head_queue(head);
720         head->func = func;
721         head->next = NULL;
722
723         local_irq_save(flags);
724         *rcu_preempt_ctrlblk.nexttail = head;
725         rcu_preempt_ctrlblk.nexttail = &head->next;
726         RCU_TRACE(rcu_preempt_ctrlblk.rcb.qlen++);
727         rcu_preempt_start_gp();  /* checks to see if GP needed. */
728         local_irq_restore(flags);
729 }
730 EXPORT_SYMBOL_GPL(call_rcu);
731
732 /*
733  * synchronize_rcu - wait until a grace period has elapsed.
734  *
735  * Control will return to the caller some time after a full grace
736  * period has elapsed, in other words after all currently executing RCU
737  * read-side critical sections have completed.  RCU read-side critical
738  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
739  * and may be nested.
740  */
741 void synchronize_rcu(void)
742 {
743         rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
744                            !lock_is_held(&rcu_lock_map) &&
745                            !lock_is_held(&rcu_sched_lock_map),
746                            "Illegal synchronize_rcu() in RCU read-side critical section");
747
748 #ifdef CONFIG_DEBUG_LOCK_ALLOC
749         if (!rcu_scheduler_active)
750                 return;
751 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
752
753         WARN_ON_ONCE(rcu_preempt_running_reader());
754         if (!rcu_preempt_blocked_readers_any())
755                 return;
756
757         /* Once we get past the fastpath checks, same code as rcu_barrier(). */
758         if (rcu_expedited)
759                 synchronize_rcu_expedited();
760         else
761                 rcu_barrier();
762 }
763 EXPORT_SYMBOL_GPL(synchronize_rcu);
764
765 static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
766 static unsigned long sync_rcu_preempt_exp_count;
767 static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
768
769 /*
770  * Return non-zero if there are any tasks in RCU read-side critical
771  * sections blocking the current preemptible-RCU expedited grace period.
772  * If there is no preemptible-RCU expedited grace period currently in
773  * progress, returns zero unconditionally.
774  */
775 static int rcu_preempted_readers_exp(void)
776 {
777         return rcu_preempt_ctrlblk.exp_tasks != NULL;
778 }
779
780 /*
781  * Report the exit from RCU read-side critical section for the last task
782  * that queued itself during or before the current expedited preemptible-RCU
783  * grace period.
784  */
785 static void rcu_report_exp_done(void)
786 {
787         wake_up(&sync_rcu_preempt_exp_wq);
788 }
789
790 /*
791  * Wait for an rcu-preempt grace period, but expedite it.  The basic idea
792  * is to rely in the fact that there is but one CPU, and that it is
793  * illegal for a task to invoke synchronize_rcu_expedited() while in a
794  * preemptible-RCU read-side critical section.  Therefore, any such
795  * critical sections must correspond to blocked tasks, which must therefore
796  * be on the ->blkd_tasks list.  So just record the current head of the
797  * list in the ->exp_tasks pointer, and wait for all tasks including and
798  * after the task pointed to by ->exp_tasks to drain.
799  */
800 void synchronize_rcu_expedited(void)
801 {
802         unsigned long flags;
803         struct rcu_preempt_ctrlblk *rpcp = &rcu_preempt_ctrlblk;
804         unsigned long snap;
805
806         barrier(); /* ensure prior action seen before grace period. */
807
808         WARN_ON_ONCE(rcu_preempt_running_reader());
809
810         /*
811          * Acquire lock so that there is only one preemptible RCU grace
812          * period in flight.  Of course, if someone does the expedited
813          * grace period for us while we are acquiring the lock, just leave.
814          */
815         snap = sync_rcu_preempt_exp_count + 1;
816         mutex_lock(&sync_rcu_preempt_exp_mutex);
817         if (ULONG_CMP_LT(snap, sync_rcu_preempt_exp_count))
818                 goto unlock_mb_ret; /* Others did our work for us. */
819
820         local_irq_save(flags);
821
822         /*
823          * All RCU readers have to already be on blkd_tasks because
824          * we cannot legally be executing in an RCU read-side critical
825          * section.
826          */
827
828         /* Snapshot current head of ->blkd_tasks list. */
829         rpcp->exp_tasks = rpcp->blkd_tasks.next;
830         if (rpcp->exp_tasks == &rpcp->blkd_tasks)
831                 rpcp->exp_tasks = NULL;
832
833         /* Wait for tail of ->blkd_tasks list to drain. */
834         if (!rcu_preempted_readers_exp()) {
835                 local_irq_restore(flags);
836         } else {
837                 rcu_initiate_boost();
838                 local_irq_restore(flags);
839                 wait_event(sync_rcu_preempt_exp_wq,
840                            !rcu_preempted_readers_exp());
841         }
842
843         /* Clean up and exit. */
844         barrier(); /* ensure expedited GP seen before counter increment. */
845         sync_rcu_preempt_exp_count++;
846 unlock_mb_ret:
847         mutex_unlock(&sync_rcu_preempt_exp_mutex);
848         barrier(); /* ensure subsequent action seen after grace period. */
849 }
850 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
851
852 /*
853  * Does preemptible RCU need the CPU to stay out of dynticks mode?
854  */
855 int rcu_preempt_needs_cpu(void)
856 {
857         return rcu_preempt_ctrlblk.rcb.rcucblist != NULL;
858 }
859
860 #else /* #ifdef CONFIG_TINY_PREEMPT_RCU */
861
862 #ifdef CONFIG_RCU_TRACE
863
864 /*
865  * Because preemptible RCU does not exist, it is not necessary to
866  * dump out its statistics.
867  */
868 static void show_tiny_preempt_stats(struct seq_file *m)
869 {
870 }
871
872 #endif /* #ifdef CONFIG_RCU_TRACE */
873
874 /*
875  * Because preemptible RCU does not exist, it never has any callbacks
876  * to check.
877  */
878 static void rcu_preempt_check_callbacks(void)
879 {
880 }
881
882 /*
883  * Because preemptible RCU does not exist, it never has any callbacks
884  * to remove.
885  */
886 static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
887 {
888 }
889
890 /*
891  * Because preemptible RCU does not exist, it never has any callbacks
892  * to process.
893  */
894 static void rcu_preempt_process_callbacks(void)
895 {
896 }
897
898 #endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */
899
900 #ifdef CONFIG_RCU_BOOST
901
902 /*
903  * Wake up rcu_kthread() to process callbacks now eligible for invocation
904  * or to boost readers.
905  */
906 static void invoke_rcu_callbacks(void)
907 {
908         have_rcu_kthread_work = 1;
909         if (rcu_kthread_task != NULL)
910                 wake_up(&rcu_kthread_wq);
911 }
912
913 #ifdef CONFIG_RCU_TRACE
914
915 /*
916  * Is the current CPU running the RCU-callbacks kthread?
917  * Caller must have preemption disabled.
918  */
919 static bool rcu_is_callbacks_kthread(void)
920 {
921         return rcu_kthread_task == current;
922 }
923
924 #endif /* #ifdef CONFIG_RCU_TRACE */
925
926 /*
927  * This kthread invokes RCU callbacks whose grace periods have
928  * elapsed.  It is awakened as needed, and takes the place of the
929  * RCU_SOFTIRQ that is used for this purpose when boosting is disabled.
930  * This is a kthread, but it is never stopped, at least not until
931  * the system goes down.
932  */
933 static int rcu_kthread(void *arg)
934 {
935         unsigned long work;
936         unsigned long morework;
937         unsigned long flags;
938
939         for (;;) {
940                 wait_event_interruptible(rcu_kthread_wq,
941                                          have_rcu_kthread_work != 0);
942                 morework = rcu_boost();
943                 local_irq_save(flags);
944                 work = have_rcu_kthread_work;
945                 have_rcu_kthread_work = morework;
946                 local_irq_restore(flags);
947                 if (work)
948                         rcu_process_callbacks(NULL);
949                 schedule_timeout_interruptible(1); /* Leave CPU for others. */
950         }
951
952         return 0;  /* Not reached, but needed to shut gcc up. */
953 }
954
955 /*
956  * Spawn the kthread that invokes RCU callbacks.
957  */
958 static int __init rcu_spawn_kthreads(void)
959 {
960         struct sched_param sp;
961
962         rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread");
963         sp.sched_priority = RCU_BOOST_PRIO;
964         sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp);
965         return 0;
966 }
967 early_initcall(rcu_spawn_kthreads);
968
969 #else /* #ifdef CONFIG_RCU_BOOST */
970
971 /* Hold off callback invocation until early_initcall() time. */
972 static int rcu_scheduler_fully_active __read_mostly;
973
974 /*
975  * Start up softirq processing of callbacks.
976  */
977 void invoke_rcu_callbacks(void)
978 {
979         if (rcu_scheduler_fully_active)
980                 raise_softirq(RCU_SOFTIRQ);
981 }
982
983 #ifdef CONFIG_RCU_TRACE
984
985 /*
986  * There is no callback kthread, so this thread is never it.
987  */
988 static bool rcu_is_callbacks_kthread(void)
989 {
990         return false;
991 }
992
993 #endif /* #ifdef CONFIG_RCU_TRACE */
994
995 static int __init rcu_scheduler_really_started(void)
996 {
997         rcu_scheduler_fully_active = 1;
998         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
999         raise_softirq(RCU_SOFTIRQ);  /* Invoke any callbacks from early boot. */
1000         return 0;
1001 }
1002 early_initcall(rcu_scheduler_really_started);
1003
1004 #endif /* #else #ifdef CONFIG_RCU_BOOST */
1005
1006 #ifdef CONFIG_DEBUG_LOCK_ALLOC
1007 #include <linux/kernel_stat.h>
1008
1009 /*
1010  * During boot, we forgive RCU lockdep issues.  After this function is
1011  * invoked, we start taking RCU lockdep issues seriously.
1012  */
1013 void __init rcu_scheduler_starting(void)
1014 {
1015         WARN_ON(nr_context_switches() > 0);
1016         rcu_scheduler_active = 1;
1017 }
1018
1019 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
1020
1021 #ifdef CONFIG_RCU_TRACE
1022
1023 #ifdef CONFIG_RCU_BOOST
1024
1025 static void rcu_initiate_boost_trace(void)
1026 {
1027         if (list_empty(&rcu_preempt_ctrlblk.blkd_tasks))
1028                 rcu_preempt_ctrlblk.n_balk_blkd_tasks++;
1029         else if (rcu_preempt_ctrlblk.gp_tasks == NULL &&
1030                  rcu_preempt_ctrlblk.exp_tasks == NULL)
1031                 rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++;
1032         else if (rcu_preempt_ctrlblk.boost_tasks != NULL)
1033                 rcu_preempt_ctrlblk.n_balk_boost_tasks++;
1034         else if (!ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))
1035                 rcu_preempt_ctrlblk.n_balk_notyet++;
1036         else
1037                 rcu_preempt_ctrlblk.n_balk_nos++;
1038 }
1039
1040 #endif /* #ifdef CONFIG_RCU_BOOST */
1041
1042 static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n)
1043 {
1044         unsigned long flags;
1045
1046         local_irq_save(flags);
1047         rcp->qlen -= n;
1048         local_irq_restore(flags);
1049 }
1050
1051 /*
1052  * Dump statistics for TINY_RCU, such as they are.
1053  */
1054 static int show_tiny_stats(struct seq_file *m, void *unused)
1055 {
1056         show_tiny_preempt_stats(m);
1057         seq_printf(m, "rcu_sched: qlen: %ld\n", rcu_sched_ctrlblk.qlen);
1058         seq_printf(m, "rcu_bh: qlen: %ld\n", rcu_bh_ctrlblk.qlen);
1059         return 0;
1060 }
1061
1062 static int show_tiny_stats_open(struct inode *inode, struct file *file)
1063 {
1064         return single_open(file, show_tiny_stats, NULL);
1065 }
1066
1067 static const struct file_operations show_tiny_stats_fops = {
1068         .owner = THIS_MODULE,
1069         .open = show_tiny_stats_open,
1070         .read = seq_read,
1071         .llseek = seq_lseek,
1072         .release = single_release,
1073 };
1074
1075 static struct dentry *rcudir;
1076
1077 static int __init rcutiny_trace_init(void)
1078 {
1079         struct dentry *retval;
1080
1081         rcudir = debugfs_create_dir("rcu", NULL);
1082         if (!rcudir)
1083                 goto free_out;
1084         retval = debugfs_create_file("rcudata", 0444, rcudir,
1085                                      NULL, &show_tiny_stats_fops);
1086         if (!retval)
1087                 goto free_out;
1088         return 0;
1089 free_out:
1090         debugfs_remove_recursive(rcudir);
1091         return 1;
1092 }
1093
1094 static void __exit rcutiny_trace_cleanup(void)
1095 {
1096         debugfs_remove_recursive(rcudir);
1097 }
1098
1099 module_init(rcutiny_trace_init);
1100 module_exit(rcutiny_trace_cleanup);
1101
1102 MODULE_AUTHOR("Paul E. McKenney");
1103 MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation");
1104 MODULE_LICENSE("GPL");
1105
1106 static void check_cpu_stall_preempt(void)
1107 {
1108 #ifdef CONFIG_TINY_PREEMPT_RCU
1109         check_cpu_stall(&rcu_preempt_ctrlblk.rcb);
1110 #endif /* #ifdef CONFIG_TINY_PREEMPT_RCU */
1111 }
1112
1113 #endif /* #ifdef CONFIG_RCU_TRACE */