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

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Message-Id: <20190822152107.adc0d4cd374fcc3eb8e148a9@linux-foundation.org>
Date:   Thu, 22 Aug 2019 15:21:07 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Joseph Qi <joseph.qi@...ux.alibaba.com>
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 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?