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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Olivier Langlois <olivier@trillion01.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        io-uring <io-uring@vger.kernel.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Jens Axboe <axboe@kernel.dk>,
        "Pavel Begunkov\>" <asml.silence@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>
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        <87h7i694ij.fsf_-_@disp2133>
        <CAHk-=wjC7GmCHTkoz2_CkgSc_Cgy19qwSQgJGXz+v2f=KT3UOw@mail.gmail.com>
        <198e912402486f66214146d4eabad8cb3f010a8e.camel@trillion01.com>
Date:   Wed, 09 Jun 2021 16:05:29 -0500
In-Reply-To: <198e912402486f66214146d4eabad8cb3f010a8e.camel@trillion01.com>
        (Olivier Langlois's message of "Wed, 09 Jun 2021 17:02:05 -0400")
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Subject: Re: [RFC] coredump: Do not interrupt dump for TIF_NOTIFY_SIGNAL
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Olivier Langlois <olivier@trillion01.com> writes:

> On Wed, 2021-06-09 at 13:33 -0700, Linus Torvalds wrote:
>> Now, the fact that we haven't cleared TIF_NOTIFY_SIGNAL for the first
>> signal is clearly the immediate cause of this, but at the same time I
>> really get the feeling that that coredump aborting code should always
>> had used fatal_signal_pending().
>
> I need clarify what does happen with the io_uring situation. If
> somehow, TIF_NOTIFY_SIGNAL wasn't cleared, I would get all the time a 0
> byte size core dump because do_coredump() does check if the dump is
> interrupted before writing a single byte.
>
> io_uring is quite a strange animal. AFAIK, the common pattern to use a
> wait_queue is to insert a task into it and then put that task to sleep
> until the waited event occur.
>
> io_uring place tasks into wait queues and then let the the task return
> to user space to do some other stuff (like core dumping). I would guess
> that it is the main reason for it using the task_work feature.
>
> So the TIF_NOTIFY_SIGNAL does get set WHILE the core dump is written.

Did you mean?

So the TIF_NOTIFY_SIGNAL does _not_ get set WHILE the core dump is written.

Eric