33e1c288da
If the freezing of tasks fails and a task is preempted in refrigerator() before calling frozen_process(), then thaw_tasks() may run before this task is frozen. In that case the task will freeze and no one will thaw it. To fix this race we can call freezing(current) in refrigerator() along with frozen_process(current) under the task_lock() which also should be taken in the error path of try_to_freeze_tasks() as well as in thaw_process(). Moreover, if thaw_process() additionally clears TIF_FREEZE for tasks that are not frozen, we can be sure that all tasks are thawed and there are no pending "freeze" requests after thaw_tasks() has run. Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl> Acked-by: Pavel Machek <pavel@ucw.cz> Cc: Gautham R Shenoy <ego@in.ibm.com> Cc: Oleg Nesterov <oleg@tv-sign.ru> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
101 lines
2.2 KiB
C
101 lines
2.2 KiB
C
/* Freezer declarations */
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#include <linux/sched.h>
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#ifdef CONFIG_PM
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/*
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* Check if a process has been frozen
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*/
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static inline int frozen(struct task_struct *p)
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{
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return p->flags & PF_FROZEN;
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}
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/*
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* Check if there is a request to freeze a process
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*/
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static inline int freezing(struct task_struct *p)
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{
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return test_tsk_thread_flag(p, TIF_FREEZE);
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}
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/*
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* Request that a process be frozen
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*/
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static inline void freeze(struct task_struct *p)
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{
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set_tsk_thread_flag(p, TIF_FREEZE);
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}
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/*
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* Sometimes we may need to cancel the previous 'freeze' request
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*/
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static inline void do_not_freeze(struct task_struct *p)
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{
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clear_tsk_thread_flag(p, TIF_FREEZE);
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}
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/*
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* Wake up a frozen process
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*
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* task_lock() is taken to prevent the race with refrigerator() which may
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* occur if the freezing of tasks fails. Namely, without the lock, if the
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* freezing of tasks failed, thaw_tasks() might have run before a task in
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* refrigerator() could call frozen_process(), in which case the task would be
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* frozen and no one would thaw it.
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*/
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static inline int thaw_process(struct task_struct *p)
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{
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task_lock(p);
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if (frozen(p)) {
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p->flags &= ~PF_FROZEN;
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task_unlock(p);
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wake_up_process(p);
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return 1;
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}
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clear_tsk_thread_flag(p, TIF_FREEZE);
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task_unlock(p);
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return 0;
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}
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/*
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* freezing is complete, mark process as frozen
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*/
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static inline void frozen_process(struct task_struct *p)
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{
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p->flags |= PF_FROZEN;
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wmb();
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clear_tsk_thread_flag(p, TIF_FREEZE);
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}
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extern void refrigerator(void);
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extern int freeze_processes(void);
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extern void thaw_processes(void);
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static inline int try_to_freeze(void)
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{
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if (freezing(current)) {
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refrigerator();
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return 1;
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} else
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return 0;
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}
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extern void thaw_some_processes(int all);
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#else
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static inline int frozen(struct task_struct *p) { return 0; }
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static inline int freezing(struct task_struct *p) { return 0; }
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static inline void freeze(struct task_struct *p) { BUG(); }
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static inline int thaw_process(struct task_struct *p) { return 1; }
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static inline void frozen_process(struct task_struct *p) { BUG(); }
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static inline void refrigerator(void) {}
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static inline int freeze_processes(void) { BUG(); return 0; }
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static inline void thaw_processes(void) {}
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static inline int try_to_freeze(void) { return 0; }
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#endif
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