lkml.org 
[lkml]   [2007]   [Jul]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Q: a bogus task_running() check in try_to_wake_up() ?
On 07/17, Ingo Molnar wrote:
>
> * Oleg Nesterov <oleg@tv-sign.ru> wrote:
>
> > try_to_wake_up:
> >
> > if (p->se.on_rq)
> > goto out_running;
> >
> > ...
> >
> > if (unlikely(task_running(rq, p)))
> > goto out_activate;
> >
> > How it possible that rq->curr has on_rq == 0 ?
> >
> > AFAICS, this can only happen if this task is rq->idle. But idle
> > threads should not sleep, we have a special "scheduling from the idle
> > thread!" check in schedule().
>
> it's also possible if an arch uses __ARCH_WANT_INTERRUPTS_ON_CTXSW,
> right?

Ah, got it. I guess you meant __ARCH_WANT_UNLOCKED_CTXSW though.

In that case schedule() drops rq->lock before the context switch, but doesn't
clear ->oncpu. So, task_running(p) means we must not activate "p" on another
CPU, otherwise it could be scheduled before the switch-in-progress completes.

Thanks a lot!

Oleg.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-07-18 18:37    [W:0.575 / U:0.220 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site