[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <b647ffbd0912022357w640bea4embe42f2a83b54220d@mail.gmail.com>
Date: Thu, 3 Dec 2009 08:57:32 +0100
From: Dmitry Adamushko <dmitry.adamushko@...il.com>
To: liu pf <kernelfans@...il.com>
Cc: linux-kernel@...r.kernel.org
Subject: Re: Should we use preempt_disable() in sleep_on_common()?
2009/12/3 liu pf <kernelfans@...il.com>:
> Hi:
>
> I am puzzled with the following scenario. Could anyone enlighten me?
>
> Thanks
> pfliu
>
>
> static long __sched
> sleep_on_common(wait_queue_head_t *q, int state, long timeout)
> {
> unsigned long flags;
> wait_queue_t wait;
>
> init_waitqueue_entry(&wait, current);
>
> __set_current_state(state);
>
> ==========>suppose that after task A set state=TASK_INTERRUPTIBLE
> , it is preempted by task B.
>
> spin_lock_irqsave(&q->lock, flags);
> ...............................................................
> }
>
> asmlinkage void __sched schedule(void)
> {
> .......................................................................................................
> if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
> if (unlikely(signal_pending_state(prev->state, prev)))
> prev->state = TASK_RUNNING;
> else
> deactivate_task(rq, prev, 1);
> =============>This will remove task A from rq, but there are no
> wait queue referring to A, so we lose A.
> switch_count = &prev->nvcsw;
> }
In this case, (preempt_count() & PREEMPT_ACTIVE) == 1(see
preempt_schedule_irq() and other use-cases of PREEMPT_ACTIVE) so we
don't enter this block.
i.e. a preempted task stays on its queue (with state != TASK_RUNNING
but that doesn't really matter).
-- Dmitry
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists