linux-kernel - Re: [PATCH] sched: idle: move need_resched check after function rcu_idle

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Message-ID: <CAJFUiJg_2AfuvDnRKc_G7N78ty5jjVAGcHFyeJbfFkHALsLubQ@mail.gmail.com>
Date:	Mon, 23 Nov 2015 09:42:06 -0800
From:	Lianwei Wang <lianwei.wang@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org,
	rjw@...ysocki.net, mingo@...hat.com
Subject: Re: [PATCH] sched: idle: move need_resched check after function rcu_idle_enter

Issue was found on ARM/Qcom platform, but I think it is applicable to
other platforms as well.  I add a BUG_ON after rcu_enter_idle to catch
it. The Qcom's cpuidle driver is not in mainline kernel yet.

On Mon, Nov 23, 2015 at 5:05 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Sat, Nov 21, 2015 at 01:02:02AM -0800, Lianwei Wang wrote:
>> The rcu_idle_endter may call wakeup_softirqd to set the need resched
>> flag on idle process. But if we don't check it after that, then the
>> cpu will enter idle state with RESCHED flag set and can not be woken
>> up by wakeup/resched call anymore.
>
> Fair enough; but which cpuidle driver did you observe that with? All the
> ones I checked test for need_resched again after this.
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