linux-kernel - Re: [6.5-rc5 regression] core dump hangs (was Re: [Bug report] fstests generic/051 (on xfs) hang on latest linux v6.5-rc5+)

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Date:   Mon, 12 Jun 2023 12:11:19 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Jens Axboe <axboe@...nel.dk>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Dave Chinner <david@...morbit.com>,
        Zorro Lang <zlang@...hat.com>, linux-xfs@...r.kernel.org,
        Mike Christie <michael.christie@...cle.com>,
        "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [6.5-rc5 regression] core dump hangs (was Re: [Bug report]
 fstests generic/051 (on xfs) hang on latest linux v6.5-rc5+)

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> On Mon, Jun 12, 2023 at 9:45 AM Jens Axboe <axboe@...nel.dk> wrote:
>>
>> You snipped the suspicion in my reply on why that exists, to avoid
>> io_wq_worker_sleeping() triggering.
>
> I'm not seeing why triggering io_wq_worker_sleeping() should even be a
> problem in the first place.
>
> I suspect that is entirely historical too, and has to do with how it
> used to do that
>
>         struct io_worker *worker = kthread_data(tsk);
>         struct io_wqe *wqe = worker->wqe;
>
> back in the bad old days of kthreads.
>
> But yeah, I don't know that code.

If it is a problem it looks like the thread shutdown can clear
"worker->flags & IO_WORKER_F_UP" rather than
"current->flags & PF_IO_WORKER".

I don't see how it makes sense for the load balancing logic for
a per-process thread pool to be running at that point.

Eric