From: Peter Zijlstra <peterz@infradead.org>
To: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: mingo@kernel.org, linux-kernel@vger.kernel.org,
linaro-kernel@lists.linaro.org, alex.shi@linaro.org
Subject: Re: [PATCH 2/4] sched: Fix race in idle_balance()
Date: Fri, 17 Jan 2014 14:33:11 +0100 [thread overview]
Message-ID: <20140117133311.GG11314@laptop.programming.kicks-ass.net> (raw)
In-Reply-To: <1389949444-14821-2-git-send-email-daniel.lezcano@linaro.org>
On Fri, Jan 17, 2014 at 10:04:02AM +0100, Daniel Lezcano wrote:
> The scheduler main function 'schedule()' checks if there are no more tasks
> on the runqueue. Then it checks if a task should be pulled in the current
> runqueue in idle_balance() assuming it will go to idle otherwise.
>
> But the idle_balance() releases the rq->lock in order to lookup in the sched
> domains and takes the lock again right after. That opens a window where
> another cpu may put a task in our runqueue, so we won't go to idle but
> we have filled the idle_stamp, thinking we will.
>
> This patch closes the window by checking if the runqueue has been modified
> but without pulling a task after taking the lock again, so we won't go to idle
> right after in the __schedule() function.
Did you actually observe this or was it found by reading the code?
next prev parent reply other threads:[~2014-01-17 13:33 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-17 9:04 [PATCH 1/4] sched: Remove 'cpu' parameter for idle_balance() Daniel Lezcano
2014-01-17 9:04 ` [PATCH 2/4] sched: Fix race in idle_balance() Daniel Lezcano
2014-01-17 13:33 ` Peter Zijlstra [this message]
2014-01-17 13:44 ` Daniel Lezcano
2014-02-11 12:15 ` [tip:sched/core] " tip-bot for Daniel Lezcano
2014-01-17 9:04 ` [PATCH 3/4] sched: Move idle_stamp up to the core Daniel Lezcano
2014-02-11 12:16 ` [tip:sched/core] sched: Move rq->idle_stamp " tip-bot for Daniel Lezcano
2014-01-17 9:04 ` [PATCH 4/4] sched: Idle task shortcut optimization Daniel Lezcano
2014-01-17 14:09 ` Peter Zijlstra
2014-01-17 15:09 ` Daniel Lezcano
2014-01-17 15:23 ` Peter Zijlstra
2014-01-17 14:26 ` Peter Zijlstra
2014-01-17 15:06 ` Daniel Lezcano
2014-01-17 15:23 ` Peter Zijlstra
2014-01-17 15:26 ` Daniel Lezcano
2014-01-17 15:33 ` Peter Zijlstra
2014-01-17 16:06 ` Daniel Lezcano
2014-01-17 16:37 ` Daniel Lezcano
2014-01-17 16:45 ` [PATCH 1/2] sched/deadline: Fix compilation error Daniel Lezcano
2014-01-17 16:45 ` [PATCH 2/2] sched: Use idle task shortcut Daniel Lezcano
2014-01-21 8:41 ` [PATCH 4/4] sched: Idle task shortcut optimization Daniel Lezcano
2014-01-21 9:06 ` Peter Zijlstra
2014-01-21 9:28 ` Daniel Lezcano
2014-02-11 12:15 ` [tip:sched/core] sched: Remove 'cpu' parameter from idle_balance( ) tip-bot for Daniel Lezcano
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