From: Oleg Nesterov <oleg@redhat.com>
To: Yasunori Goto <y-goto@jp.fujitsu.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@elte.hu>,
Hiroyuki KAMEZAWA <kamezawa.hiroyu@jp.fujitsu.com>,
Motohiro Kosaki <kosaki.motohiro@jp.fujitsu.com>,
Linux Kernel ML <linux-kernel@vger.kernel.org>
Subject: Re: [BUG] TASK_DEAD task is able to be woken up in special condition
Date: Fri, 6 Jan 2012 14:48:34 +0100 [thread overview]
Message-ID: <20120106134834.GA19462@redhat.com> (raw)
In-Reply-To: <20120106192256.AB15.E1E9C6FF@jp.fujitsu.com>
On 01/06, Yasunori Goto wrote:
>
> +change_task_state_cmpxchg(struct task_struct *p, unsigned int target_state,
> + unsigned int new)
> {
> - trace_sched_wakeup(p, true);
> - check_preempt_curr(rq, p, wake_flags);
> + unsigned int old, tmp;
>
> - p->state = TASK_RUNNING;
> + old = p->state;
> +
> + while (1) {
> + if (old == new)
> + return 1;
> +
> + if (unlikely(!(old & target_state)))
> + return 0;
> +
> + tmp = cmpxchg(&p->state, old, new);
> + if (likely(tmp == old))
> + return 1;
> +
> + old = tmp;
> + }
I do not really think we should retry if cmpxchg fails. The state was
changed after initial check, we can pretend it was changed after we
change it succesfully.
> @@ -2828,11 +2883,18 @@ try_to_wake_up(struct task_struct *p, un
> if (!(p->state & state))
> goto out;
>
> - success = 1; /* we're going to change ->state */
> cpu = task_cpu(p);
>
> - if (p->on_rq && ttwu_remote(p, wake_flags))
> - goto stat;
> + if (p->on_rq) {
> + int ret;
> + ret = ttwu_remote(p, state, wake_flags);
> + if (likely(ret == 1)) {
> + success = 1;
> + goto stat;
> + } else if (unlikely(ret < 0))
> + goto out;
> + }
> + success = 1; /* we're going to change ->state */
But this is not enough, you should also recheck the state below. Although
in this case you do not need atomic ops, the target can do nothing with
its ->state.
Anyway. I have to agree with Peter even if I suggested this initially.
This adds the unpleasant complications. Hopefully you found the only
case when the spurious wakeup really hurts, probably it is better to
fix do_exit().
Oleg.
next prev parent reply other threads:[~2012-01-06 13:54 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-22 0:42 [BUG] TASK_DEAD task is able to be woken up in special condition Yasunori Goto
2011-12-22 2:14 ` KOSAKI Motohiro
2011-12-22 8:22 ` Yasunori Goto
2011-12-22 20:02 ` KOSAKI Motohiro
2011-12-23 9:49 ` Peter Zijlstra
2011-12-23 15:41 ` Oleg Nesterov
2011-12-26 8:23 ` Yasunori Goto
2011-12-26 17:11 ` Oleg Nesterov
2011-12-27 6:48 ` Yasunori Goto
2012-01-06 10:22 ` Yasunori Goto
2012-01-06 11:01 ` Peter Zijlstra
2012-01-06 12:01 ` Yasunori Goto
2012-01-06 12:43 ` Peter Zijlstra
2012-01-06 14:12 ` Oleg Nesterov
2012-01-06 14:19 ` Oleg Nesterov
2012-01-07 1:31 ` Yasunori Goto
2012-01-16 11:51 ` Yasunori Goto
2012-01-16 13:38 ` Peter Zijlstra
2012-01-17 8:40 ` Yasunori Goto
2012-01-17 9:06 ` Ingo Molnar
2012-01-17 15:12 ` Oleg Nesterov
2012-01-18 9:42 ` Ingo Molnar
2012-01-18 14:20 ` Oleg Nesterov
2012-01-24 10:19 ` Peter Zijlstra
2012-01-24 10:55 ` Peter Zijlstra
2012-01-24 17:25 ` KOSAKI Motohiro
2012-01-25 15:45 ` Oleg Nesterov
2012-01-25 16:51 ` Peter Zijlstra
2012-01-25 17:43 ` Oleg Nesterov
2012-01-26 15:32 ` Peter Zijlstra
2012-01-26 16:26 ` Oleg Nesterov
2012-01-27 8:59 ` Peter Zijlstra
2012-01-24 10:11 ` Peter Zijlstra
2012-01-26 9:39 ` Ingo Molnar
2012-01-28 12:03 ` [tip:sched/core] sched: Fix ancient race in do_exit() tip-bot for Yasunori Goto
2012-01-28 21:12 ` Linus Torvalds
2012-01-29 16:07 ` Oleg Nesterov
2012-01-29 17:44 ` Linus Torvalds
2012-01-29 18:28 ` Linus Torvalds
2012-01-29 18:59 ` Oleg Nesterov
2012-01-30 16:27 ` Linus Torvalds
2012-01-06 13:48 ` Oleg Nesterov [this message]
2011-12-28 21:07 ` [BUG] TASK_DEAD task is able to be woken up in special condition KOSAKI Motohiro
2012-01-24 10:23 ` Peter Zijlstra
2012-01-24 18:01 ` KOSAKI Motohiro
2012-01-25 6:15 ` Mike Galbraith
2012-01-26 21:24 ` KOSAKI Motohiro
2012-01-25 10:10 ` Peter Zijlstra
2012-01-26 20:25 ` [tip:sched/urgent] sched: Fix rq->nr_uninterruptible update race tip-bot for Peter Zijlstra
2012-01-27 5:20 ` Rakib Mullick
2012-01-27 8:19 ` Peter Zijlstra
2012-01-27 14:11 ` Rakib Mullick
2012-01-26 21:21 ` [BUG] TASK_DEAD task is able to be woken up in special condition KOSAKI Motohiro
2012-01-27 8:21 ` Peter Zijlstra
2011-12-26 6:52 ` Yasunori Goto
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