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Message-ID: <8880aac1e81ac38928f58da2d29057cb69139d8c.camel@trillion01.com>
Subject: Re: [RFC] coredump: Do not interrupt dump for TIF_NOTIFY_SIGNAL
From: Olivier Langlois <olivier@trillion01.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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"Pavel Begunkov>" <asml.silence@gmail.com>,
Oleg Nesterov <oleg@redhat.com>
Date: Wed, 09 Jun 2021 17:56:30 -0400
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On Wed, 2021-06-09 at 17:26 -0400, Olivier Langlois wrote:
> On Wed, 2021-06-09 at 16:05 -0500, Eric W. Biederman wrote:
> > >
> > > 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.
> >
> >
> Absolutely not. I did really mean what I have said. Bear with me
> that,
> I am not qualifying myself as an expert kernel dev yet so feel free
> to
> correct me if I say some heresy...
>
> io_uring is placing my task in my TCP socket wait queue because it
> wants to read data from it.
>
> The task returns to user space and core dump with a SEGV.
>
> now my understanding is that the code that is waking up tasks, it is
> the NIC driver interrupt handler which can occur while the core dump
> is
> written.
>
> does that make sense?
>
> my testing is telling me that this is exactly what happens...
>
>
Another thing to know is that dump_interrupted() isn't only called from
do_coredump().
At first, I did the mistake to think that if dump_interrupt() was
returning false when called from do_coredump() all was good.
It is not the case. dump_interrupted() is also called from dump_emit()
which is called from several places by functions inside binfmt_elf.c
So dump_interrupted() is called several times during the coredump
generation.