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Subject: Re: [PATCH 2/2] coredump: Allow coredumps to pipes to work with
io_uring
From: Olivier Langlois <olivier@trillion01.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>,
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Cc: Pavel Begunkov <asml.silence@gmail.com>,
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Linus Torvalds <torvalds@linux-foundation.org>
Date: Mon, 22 Aug 2022 23:35:37 -0400
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On Mon, 2022-08-22 at 17:16 -0400, Olivier Langlois wrote:
>
> What is stopping the task calling do_coredump() to be interrupted and
> call task_work_add() from the interrupt context?
>
> This is precisely what I was experiencing last summer when I did work
> on this issue.
>
> My understanding of how async I/O works with io_uring is that the
> task
> is added to a wait queue without being put to sleep and when the
> io_uring callback is called from the interrupt context,
> task_work_add()
> is called so that the next time io_uring syscall is invoked, pending
> work is processed to complete the I/O.
>
> So if:
>
> 1. io_uring request is initiated AND the task is in a wait queue
> 2. do_coredump() is called before the I/O is completed
>
> IMHO, this is how you end up having task_work_add() called while the
> coredump is generated.
>
I forgot to add that I have experienced the issue with TCP/IP I/O.
I suspect that with a TCP socket, the race condition window is much
larger than if it was disk I/O and this might make it easier to
reproduce the issue this way...