Re: [BUG] TASK_DEAD task is able to be woken up in special condition

Oleg Nesterov
2011-12-26T17:17:39Z

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.