linux-kernel - Re: [PATCH v3] psi: get poll_work to run when calling poll syscall next time

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Message-ID: <8a093924-98ea-de13-554d-5f5b6ee63536@linux.alibaba.com>
Date:   Fri, 23 Aug 2019 08:53:09 +0800
From:   Joseph Qi <joseph.qi@...ux.alibaba.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Jason Xing <kerneljasonxing@...ux.alibaba.com>,
        Caspar Zhang <caspar@...ux.alibaba.com>
Subject: Re: [PATCH v3] psi: get poll_work to run when calling poll syscall
 next time



On 19/8/23 06:21, Andrew Morton wrote:
> On Wed, 21 Aug 2019 11:26:25 +0800 Joseph Qi <joseph.qi@...ux.alibaba.com> wrote:
> 
>> Only when calling the poll syscall the first time can user
>> receive POLLPRI correctly. After that, user always fails to
>> acquire the event signal.
>>
>> Reproduce case:
>> 1. Get the monitor code in Documentation/accounting/psi.txt
>> 2. Run it, and wait for the event triggered.
>> 3. Kill and restart the process.
>>
>> The question is why we can end up with poll_scheduled = 1 but the work
>> not running (which would reset it to 0). And the answer is because the
>> scheduling side sees group->poll_kworker under RCU protection and then
>> schedules it, but here we cancel the work and destroy the worker. The
>> cancel needs to pair with resetting the poll_scheduled flag.
> 
> Should this be backported into -stable kernels?
> 
Sorry for missing that, should I resend it with cc stable tag?

Thanks,
Joseph