Re: [BUG] TASK_DEAD task is able to be woken up in special condition
From: KOSAKI Motohiro
Date: Wed Dec 28 2011 - 16:07:55 EST
(12/26/11 12:11 PM), Oleg Nesterov wrote:
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.
Could you point the discussion?
I don't understand yet how it occurred...
Suppose that the task T does
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.
I looked at scheduler code today briefly. now I'm afraid following code
have similar race.
Can't following schenario be happen?
task->state = TASK_UNINTERRUPTIBLE;
Totally, nr_uninterruptible wasn't incremented.
I'm still not sure. I need to read more sched code.
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