Root/kernel/rcutiny.c

1/*
2 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
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, 2008
19 *
20 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
21 *
22 * For detailed explanation of Read-Copy Update mechanism see -
23 * Documentation/RCU
24 */
25#include <linux/completion.h>
26#include <linux/interrupt.h>
27#include <linux/notifier.h>
28#include <linux/rcupdate.h>
29#include <linux/kernel.h>
30#include <linux/export.h>
31#include <linux/mutex.h>
32#include <linux/sched.h>
33#include <linux/types.h>
34#include <linux/init.h>
35#include <linux/time.h>
36#include <linux/cpu.h>
37#include <linux/prefetch.h>
38
39#ifdef CONFIG_RCU_TRACE
40#include <trace/events/rcu.h>
41#endif /* #else #ifdef CONFIG_RCU_TRACE */
42
43#include "rcu.h"
44
45/* Forward declarations for rcutiny_plugin.h. */
46struct rcu_ctrlblk;
47static void invoke_rcu_callbacks(void);
48static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
49static void rcu_process_callbacks(struct softirq_action *unused);
50static void __call_rcu(struct rcu_head *head,
51               void (*func)(struct rcu_head *rcu),
52               struct rcu_ctrlblk *rcp);
53
54#include "rcutiny_plugin.h"
55
56static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
57
58/* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
59static void rcu_idle_enter_common(long long oldval)
60{
61    if (rcu_dynticks_nesting) {
62        RCU_TRACE(trace_rcu_dyntick("--=",
63                        oldval, rcu_dynticks_nesting));
64        return;
65    }
66    RCU_TRACE(trace_rcu_dyntick("Start", oldval, rcu_dynticks_nesting));
67    if (!is_idle_task(current)) {
68        struct task_struct *idle = idle_task(smp_processor_id());
69
70        RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
71                        oldval, rcu_dynticks_nesting));
72        ftrace_dump(DUMP_ALL);
73        WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
74              current->pid, current->comm,
75              idle->pid, idle->comm); /* must be idle task! */
76    }
77    rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
78}
79
80/*
81 * Enter idle, which is an extended quiescent state if we have fully
82 * entered that mode (i.e., if the new value of dynticks_nesting is zero).
83 */
84void rcu_idle_enter(void)
85{
86    unsigned long flags;
87    long long oldval;
88
89    local_irq_save(flags);
90    oldval = rcu_dynticks_nesting;
91    WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
92    if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
93        DYNTICK_TASK_NEST_VALUE)
94        rcu_dynticks_nesting = 0;
95    else
96        rcu_dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
97    rcu_idle_enter_common(oldval);
98    local_irq_restore(flags);
99}
100EXPORT_SYMBOL_GPL(rcu_idle_enter);
101
102/*
103 * Exit an interrupt handler towards idle.
104 */
105void rcu_irq_exit(void)
106{
107    unsigned long flags;
108    long long oldval;
109
110    local_irq_save(flags);
111    oldval = rcu_dynticks_nesting;
112    rcu_dynticks_nesting--;
113    WARN_ON_ONCE(rcu_dynticks_nesting < 0);
114    rcu_idle_enter_common(oldval);
115    local_irq_restore(flags);
116}
117
118/* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
119static void rcu_idle_exit_common(long long oldval)
120{
121    if (oldval) {
122        RCU_TRACE(trace_rcu_dyntick("++=",
123                        oldval, rcu_dynticks_nesting));
124        return;
125    }
126    RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting));
127    if (!is_idle_task(current)) {
128        struct task_struct *idle = idle_task(smp_processor_id());
129
130        RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
131              oldval, rcu_dynticks_nesting));
132        ftrace_dump(DUMP_ALL);
133        WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
134              current->pid, current->comm,
135              idle->pid, idle->comm); /* must be idle task! */
136    }
137}
138
139/*
140 * Exit idle, so that we are no longer in an extended quiescent state.
141 */
142void rcu_idle_exit(void)
143{
144    unsigned long flags;
145    long long oldval;
146
147    local_irq_save(flags);
148    oldval = rcu_dynticks_nesting;
149    WARN_ON_ONCE(rcu_dynticks_nesting < 0);
150    if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK)
151        rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
152    else
153        rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
154    rcu_idle_exit_common(oldval);
155    local_irq_restore(flags);
156}
157EXPORT_SYMBOL_GPL(rcu_idle_exit);
158
159/*
160 * Enter an interrupt handler, moving away from idle.
161 */
162void rcu_irq_enter(void)
163{
164    unsigned long flags;
165    long long oldval;
166
167    local_irq_save(flags);
168    oldval = rcu_dynticks_nesting;
169    rcu_dynticks_nesting++;
170    WARN_ON_ONCE(rcu_dynticks_nesting == 0);
171    rcu_idle_exit_common(oldval);
172    local_irq_restore(flags);
173}
174
175#ifdef CONFIG_PROVE_RCU
176
177/*
178 * Test whether RCU thinks that the current CPU is idle.
179 */
180int rcu_is_cpu_idle(void)
181{
182    return !rcu_dynticks_nesting;
183}
184EXPORT_SYMBOL(rcu_is_cpu_idle);
185
186#endif /* #ifdef CONFIG_PROVE_RCU */
187
188/*
189 * Test whether the current CPU was interrupted from idle. Nested
190 * interrupts don't count, we must be running at the first interrupt
191 * level.
192 */
193int rcu_is_cpu_rrupt_from_idle(void)
194{
195    return rcu_dynticks_nesting <= 0;
196}
197
198/*
199 * Helper function for rcu_sched_qs() and rcu_bh_qs().
200 * Also irqs are disabled to avoid confusion due to interrupt handlers
201 * invoking call_rcu().
202 */
203static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
204{
205    if (rcp->rcucblist != NULL &&
206        rcp->donetail != rcp->curtail) {
207        rcp->donetail = rcp->curtail;
208        return 1;
209    }
210
211    return 0;
212}
213
214/*
215 * Record an rcu quiescent state. And an rcu_bh quiescent state while we
216 * are at it, given that any rcu quiescent state is also an rcu_bh
217 * quiescent state. Use "+" instead of "||" to defeat short circuiting.
218 */
219void rcu_sched_qs(int cpu)
220{
221    unsigned long flags;
222
223    local_irq_save(flags);
224    if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
225        rcu_qsctr_help(&rcu_bh_ctrlblk))
226        invoke_rcu_callbacks();
227    local_irq_restore(flags);
228}
229
230/*
231 * Record an rcu_bh quiescent state.
232 */
233void rcu_bh_qs(int cpu)
234{
235    unsigned long flags;
236
237    local_irq_save(flags);
238    if (rcu_qsctr_help(&rcu_bh_ctrlblk))
239        invoke_rcu_callbacks();
240    local_irq_restore(flags);
241}
242
243/*
244 * Check to see if the scheduling-clock interrupt came from an extended
245 * quiescent state, and, if so, tell RCU about it. This function must
246 * be called from hardirq context. It is normally called from the
247 * scheduling-clock interrupt.
248 */
249void rcu_check_callbacks(int cpu, int user)
250{
251    if (user || rcu_is_cpu_rrupt_from_idle())
252        rcu_sched_qs(cpu);
253    else if (!in_softirq())
254        rcu_bh_qs(cpu);
255    rcu_preempt_check_callbacks();
256}
257
258/*
259 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
260 * whose grace period has elapsed.
261 */
262static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
263{
264    char *rn = NULL;
265    struct rcu_head *next, *list;
266    unsigned long flags;
267    RCU_TRACE(int cb_count = 0);
268
269    /* If no RCU callbacks ready to invoke, just return. */
270    if (&rcp->rcucblist == rcp->donetail) {
271        RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1));
272        RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
273                          ACCESS_ONCE(rcp->rcucblist),
274                          need_resched(),
275                          is_idle_task(current),
276                          rcu_is_callbacks_kthread()));
277        return;
278    }
279
280    /* Move the ready-to-invoke callbacks to a local list. */
281    local_irq_save(flags);
282    RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
283    list = rcp->rcucblist;
284    rcp->rcucblist = *rcp->donetail;
285    *rcp->donetail = NULL;
286    if (rcp->curtail == rcp->donetail)
287        rcp->curtail = &rcp->rcucblist;
288    rcu_preempt_remove_callbacks(rcp);
289    rcp->donetail = &rcp->rcucblist;
290    local_irq_restore(flags);
291
292    /* Invoke the callbacks on the local list. */
293    RCU_TRACE(rn = rcp->name);
294    while (list) {
295        next = list->next;
296        prefetch(next);
297        debug_rcu_head_unqueue(list);
298        local_bh_disable();
299        __rcu_reclaim(rn, list);
300        local_bh_enable();
301        list = next;
302        RCU_TRACE(cb_count++);
303    }
304    RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
305    RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count, 0, need_resched(),
306                      is_idle_task(current),
307                      rcu_is_callbacks_kthread()));
308}
309
310static void rcu_process_callbacks(struct softirq_action *unused)
311{
312    __rcu_process_callbacks(&rcu_sched_ctrlblk);
313    __rcu_process_callbacks(&rcu_bh_ctrlblk);
314    rcu_preempt_process_callbacks();
315}
316
317/*
318 * Wait for a grace period to elapse. But it is illegal to invoke
319 * synchronize_sched() from within an RCU read-side critical section.
320 * Therefore, any legal call to synchronize_sched() is a quiescent
321 * state, and so on a UP system, synchronize_sched() need do nothing.
322 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the
323 * benefits of doing might_sleep() to reduce latency.)
324 *
325 * Cool, huh? (Due to Josh Triplett.)
326 *
327 * But we want to make this a static inline later. The cond_resched()
328 * currently makes this problematic.
329 */
330void synchronize_sched(void)
331{
332    rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
333               !lock_is_held(&rcu_lock_map) &&
334               !lock_is_held(&rcu_sched_lock_map),
335               "Illegal synchronize_sched() in RCU read-side critical section");
336    cond_resched();
337}
338EXPORT_SYMBOL_GPL(synchronize_sched);
339
340/*
341 * Helper function for call_rcu() and call_rcu_bh().
342 */
343static void __call_rcu(struct rcu_head *head,
344               void (*func)(struct rcu_head *rcu),
345               struct rcu_ctrlblk *rcp)
346{
347    unsigned long flags;
348
349    debug_rcu_head_queue(head);
350    head->func = func;
351    head->next = NULL;
352
353    local_irq_save(flags);
354    *rcp->curtail = head;
355    rcp->curtail = &head->next;
356    RCU_TRACE(rcp->qlen++);
357    local_irq_restore(flags);
358}
359
360/*
361 * Post an RCU callback to be invoked after the end of an RCU-sched grace
362 * period. But since we have but one CPU, that would be after any
363 * quiescent state.
364 */
365void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
366{
367    __call_rcu(head, func, &rcu_sched_ctrlblk);
368}
369EXPORT_SYMBOL_GPL(call_rcu_sched);
370
371/*
372 * Post an RCU bottom-half callback to be invoked after any subsequent
373 * quiescent state.
374 */
375void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
376{
377    __call_rcu(head, func, &rcu_bh_ctrlblk);
378}
379EXPORT_SYMBOL_GPL(call_rcu_bh);
380

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