Messages in this thread | | | Date | Wed, 28 Dec 2011 16:07:47 -0500 | From | KOSAKI Motohiro <> | Subject | Re: [BUG] TASK_DEAD task is able to be woken up in special condition |
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(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. >> >> 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.
Hi
I looked at scheduler code today briefly. now I'm afraid following code have similar race.
if (task_contributes_to_load(p)) rq->nr_uninterruptible--;
Can't following schenario be happen?
CPU0 CPU1 -------------------------------------------------------- deactivate_task() task->state = TASK_UNINTERRUPTIBLE; activate_task() rq->nr_uninterruptible--;
schedule() deactivate_task() rq->nr_uninterruptible++;
Totally, nr_uninterruptible wasn't incremented.
I'm still not sure. I need to read more sched code.
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