linux-kernel - Re: [RFC] coredump: Do not interrupt dump for TIF_NOTIFY

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Message-ID: <87eeda7nqe.fsf@disp2133>
Date:   Wed, 09 Jun 2021 16:05:29 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Olivier Langlois <olivier@...llion01.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        io-uring <io-uring@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>,
        "Pavel Begunkov\>" <asml.silence@...il.com>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [RFC] coredump: Do not interrupt dump for TIF_NOTIFY_SIGNAL

Olivier Langlois <olivier@...llion01.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