8a102eed9c
Currently, to tell a task that it should go to the refrigerator, we set the PF_FREEZE flag for it and send a fake signal to it. Unfortunately there are two SMP-related problems with this approach. First, a task running on another CPU may be updating its flags while the freezer attempts to set PF_FREEZE for it and this may leave the task's flags in an inconsistent state. Second, there is a potential race between freeze_process() and refrigerator() in which freeze_process() running on one CPU is reading a task's PF_FREEZE flag while refrigerator() running on another CPU has just set PF_FROZEN for the same task and attempts to reset PF_FREEZE for it. If the refrigerator wins the race, freeze_process() will state that PF_FREEZE hasn't been set for the task and will set it unnecessarily, so the task will go to the refrigerator once again after it's been thawed. To solve first of these problems we need to stop using PF_FREEZE to tell tasks that they should go to the refrigerator. Instead, we can introduce a special TIF_*** flag and use it for this purpose, since it is allowed to change the other tasks' TIF_*** flags and there are special calls for it. To avoid the freeze_process()-refrigerator() race we can make freeze_process() to always check the task's PF_FROZEN flag after it's read its "freeze" flag. We should also make sure that refrigerator() will always reset the task's "freeze" flag after it's set PF_FROZEN for it. Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl> Acked-by: Pavel Machek <pavel@ucw.cz> Cc: Russell King <rmk@arm.linux.org.uk> Cc: David Howells <dhowells@redhat.com> Cc: Andi Kleen <ak@muc.de> Cc: "Luck, Tony" <tony.luck@intel.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Paul Mundt <lethal@linux-sh.org> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
91 lines
1.8 KiB
C
91 lines
1.8 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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static inline int thaw_process(struct task_struct *p)
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{
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if (frozen(p)) {
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p->flags &= ~PF_FROZEN;
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wake_up_process(p);
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return 1;
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}
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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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