linux-kernel - Re: [PATCH v5] locking/rwsem: Make handoff bit handling more consistent

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Message-ID: <CAD=FV=UyAecgOfiA18WoA+Dd7DxwD7v1RbjrKUs9=LqrZ6C70g@mail.gmail.com>
Date:   Fri, 5 Aug 2022 12:16:18 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Hillf Danton <hdanton@...a.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>,
        Davidlohr Bueso <dave@...olabs.net>, MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5] locking/rwsem: Make handoff bit handling more consistent

Hi,

On Fri, Aug 5, 2022 at 12:02 PM Waiman Long <longman@...hat.com> wrote:
>
>
> On 8/5/22 13:14, Doug Anderson wrote:
> > Hi,
> >
> > On Fri, Jul 22, 2022 at 5:17 PM Hillf Danton <hdanton@...a.com> wrote:
> >> On Fri, 22 Jul 2022 07:02:42 -0700 Doug Anderson wrote:
> >>> Thanks! I added this diff to your previous diff and my simple test
> >>> still passes and I don't see your WARN_ON triggered.
> >> Thanks!
> >>> How do we move forward? Are you going to officially submit a patch
> >>> with both of your diffs squashed together? Are we waiting for
> >>> additional review from someone?
> >> Given it is not unusual for us to miss anything important, lets take
> >> a RWSEM_WAIT_TIMEOUT nap now or two.
> > It appears that another fix has landed in the meantime. Commit
> > 6eebd5fb2083 ("locking/rwsem: Allow slowpath writer to ignore handoff
> > bit if not set by first waiter").
> >
> > ...unfortunately with that patch my test cases still hangs. :(
>
> The aim of commit 6eebd5fb2083 ("locking/rwsem: Allow slowpath writer to
> ignore handoff bit if not set by first waiter") is to restore slowpath
> writer behavior to be the same as before commit d257cc8cb8d5
> ("locking/rwsem: Make handoff bit handling more consistent").

Ah, OK. I just saw another fix to the same commit and assumed that
perhaps it was intended to address the same issue.


> If the hang still exists, there may be other cause for it. Could you
> share more information about what the test case is doing and any kernel
> splat that you have?

It's all described in my earlier reply including my full test case:

https://lore.kernel.org/r/CAD=FV=URCo5xv3k3jWbxV1uRkUU5k6bcnuB1puZhxayEyVc6-A@mail.gmail.com

Previously I tested Hillf's patches and they fixed it for me.

-Doug