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

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Message-Id: <20190822161738.02297ead0abd424c44fb33b9@linux-foundation.org>
Date:   Thu, 22 Aug 2019 16:17:38 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Jason Xing <kerneljasonxing@...ux.alibaba.com>,
        Caspar Zhang <caspar@...ux.alibaba.com>, stable@...r.kernel.org
Subject: Re: [PATCH v3] psi: get poll_work to run when calling poll syscall
 next time

On Thu, 22 Aug 2019 16:11:15 -0700 Suren Baghdasaryan <surenb@...gle.com> wrote:

> On Thu, Aug 22, 2019 at 3:21 PM Andrew Morton <akpm@...ux-foundation.org> 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?
> 
> Adding GregKH and stable@...r.kernel.org
> 
> I was able to cleanly apply this patch to stable master and
> linux-5.2.y branches (these are the only branches that have psi
> triggers).
> Greg, Andrew got this patch into -mm tree. Please advise on how we
> should proceed to land it in stable 5.2.y and master.

That isn't the point - we know how to merge patches ;)

What I'm asking is whether it is desirable that -stable kernels have
this patch.  It certainly sounds like it from the changelog, so I'm
wondering if the omission of cc:stable was intentional?