linux-kernel - Re: [PATCH] fs: process fput task_work with TWA

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Message-ID: <CAD=FV=WJzNEf+=H2_Eyz3HRnv+0hW5swikg=hFMkHxGb569Bpw@mail.gmail.com>
Date:   Thu, 7 Jan 2021 14:17:27 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Oleg Nesterov <oleg@...hat.com>,
        Song Liu <songliubraving@...com>
Subject: Re: [PATCH] fs: process fput task_work with TWA_SIGNAL

Hi,

On Tue, Jan 5, 2021 at 10:30 AM Jens Axboe <axboe@...nel.dk> wrote:
>
> Song reported a boot regression in a kvm image with 5.11-rc, and bisected
> it down to the below patch. Debugging this issue, turns out that the boot
> stalled when a task is waiting on a pipe being released. As we no longer
> run task_work from get_signal() unless it's queued with TWA_SIGNAL, the
> task goes idle without running the task_work. This prevents ->release()
> from being called on the pipe, which another boot task is waiting on.
>
> Use TWA_SIGNAL for the file fput work to ensure it's run before the task
> goes idle.
>
> Fixes: 98b89b649fce ("signal: kill JOBCTL_TASK_WORK")
> Reported-by: Song Liu <songliubraving@...com>
> Signed-off-by: Jens Axboe <axboe@...nel.dk>

I just spend a bit of time bisecting and landed on commit 98b89b649fce
("signal: kill JOBCTL_TASK_WORK") causing my failure to bootup
mainline.  Your patch fixes my problem.  I haven't done any analysis
of the code--just testing, thus:

Tested-by: Douglas Anderson <dianders@...omium.org>