Messages in this thread | | | Subject | Re: [BUG] TASK_DEAD task is able to be woken up in special condition | From | Peter Zijlstra <> | Date | Fri, 27 Jan 2012 09:59:41 +0100 |
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On Thu, 2012-01-26 at 17:26 +0100, Oleg Nesterov wrote: > On 01/26, Peter Zijlstra wrote:
> > However I think your proposal: > > > > > for (;;) { > > > tsk->state = TASK_DEAD; > > > schedule(); > > > } > > > > should equally work, if we hit the race and call schedule() with ->state > > = TASK_RUNNING, > > Yes, in this case everything is fine, but we can shedule() with TASK_DEAD > state. preempt_disable() can't (and shouldn't) prevent deactivate_task(). > > To simplify, try_to_wake_up() does > > spin_lock(pi_lock); > > if (!(p->state & state)) > goto out; > > /* WINDOW */ > > if (p->on_rq) { > ... everything is fine ... > } > > p->state = TASK_WAKING; > ttwu_queue(p, cpu); > > And the exiting task does > > // but do not sleep ... > current->state = TASK_UNINTERRUPTIBLE; > // ttwu() checks ->state > ... > tsk->state = TASK_DEAD; > schedule(); > -> deactivate_task(); > -> tsk->on_rq = 0; > -> finish_task_switch(); > > // ttwu() checks ->on_rq > > In theory it can do this all in the WINDOW above. In this case we > can wake it up again, after finish_task_switch()-put_task_struct(). > > No?
Yes, bugger. Ok I'll queue Yasunori-san's patch as is.
Thanks everyone!
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