Messages in this thread | | | Date | Tue, 27 Dec 2011 15:48:29 +0900 | From | Yasunori Goto <> | Subject | Re: [BUG] TASK_DEAD task is able to be woken up in special condition |
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> On 12/26, Yasunori Goto wrote: > > > > > > > > IIRC, this was already discussed a bit. Say, try_to_wake_up(TASK_INTERRUPTIBLE) > > > can wakeup a TASK_UNINTERRUPTIBLE task if it temporary sets INTERRUPTIBLE but > > > doesn't call schedule() in this state. > > > > Oleg-san, > > > > Could you point the discussion? > > I don't understand yet how it occurred... > > Suppose that the task T does > > set_current_state(TASK_INTERRUPTIBLE); > > set_current_state(TASK_UNINTERRUPTIBLE); > schedule(); > > try_to_wake_up(TASK_UNINTERRUPTIBLE) in between can observe this task > in TASK_INTERRUPTIBLE state. Then it can set RUNNING/WAKING after T > sets ->state = TASK_UNINTERRUPTIBLE. > > For example, this is possibly if T simply does wait_event() twice when > the the 1st wait_event() doesn't sleep. > > Basically this is the same race you described, but I think you found > the case when we can't tolerate the spurious wakeup. > > Oleg. > > On 12/26, Yasunori Goto wrote: > > > > > > > > IIRC, this was already discussed a bit. Say, try_to_wake_up(TASK_INTERRUPTIBLE) > > > can wakeup a TASK_UNINTERRUPTIBLE task if it temporary sets INTERRUPTIBLE but > > > doesn't call schedule() in this state. > > > > Oleg-san, > > > > Could you point the discussion? > > I don't understand yet how it occurred... > > Suppose that the task T does > > set_current_state(TASK_INTERRUPTIBLE); > > set_current_state(TASK_UNINTERRUPTIBLE); > schedule(); > > try_to_wake_up(TASK_UNINTERRUPTIBLE) in between can observe this task > in TASK_INTERRUPTIBLE state. Then it can set RUNNING/WAKING after T > sets ->state = TASK_UNINTERRUPTIBLE. > > For example, this is possibly if T simply does wait_event() twice when > the the 1st wait_event() doesn't sleep. > > Basically this is the same race you described, but I think you found > the case when we can't tolerate the spurious wakeup.
Thanks.
I suppose your idea which uses cmpxchg(old_state, RUNNING) is best way. I'll remake my patch.
> > Oleg. >
-- Yasunori Goto
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