Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <8735v3ex3h.ffs@nanos.tec.linutronix.de> <3C41339D-29A2-4AB1-958F-19DB0A92D8D7@amacapital.net>
 <CAHk-=wh0KoEZXPYMGkfkeVEerSCEF1AiCZSvz9TRrx=Kj74D+Q@mail.gmail.com>
 <CALCETrV9bCenqzzaW6Ra18tCvNP-my09decTjmLDVZZAQxR6VA@mail.gmail.com>
 <CAHk-=wgo6XEz3VQ9ntqzWLR3-hm1YXrXUz4_heDs4wcLe9NYvA@mail.gmail.com>
 <d26e3a82-8a2c-7354-d36b-cac945c208c7@kernel.dk> <CALCETrWmhquicE2C=G2Hmwfj4VNypXVxY-K3CWOkyMe9Edv88A@mail.gmail.com>
 <CAHk-=wgqK0qUskrzeWXmChErEm32UiOaUmynWdyrjAwNzkDKaw@mail.gmail.com>
 <8735v3jujv.ffs@nanos.tec.linutronix.de> <CAHk-=wi4Dyg_Z70J_hJbtFLPQDG+Zx3dP2jB5QrOdZC6W6j4Gw@mail.gmail.com>
 <12710fda-1732-ee55-9ac1-0df9882aa71b@samba.org> <CAHk-=wiR7c-UHh_3Rj-EU8=AbURKchnMFJWW7=5EH=qEUDT8wg@mail.gmail.com>
 <59ea3b5a-d7b3-b62e-cc83-1f32a83c4ac2@kernel.dk> <17471c9fec18765449ef3a5a4cddc23561b97f52.camel@trillion01.com>
In-Reply-To: <17471c9fec18765449ef3a5a4cddc23561b97f52.camel@trillion01.com>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 12 May 2021 10:44:40 -0700
Message-ID: <CAHk-=whoJCocFsQ7+Sqq=dkuzHE+RXxvRdd4ZvyYqnsKBqsKAA@mail.gmail.com>
Subject: Re: [PATCH] io_thread/x86: don't reset 'cs', 'ss', 'ds' and 'es'
 registers for io_threads
To:     Olivier Langlois <olivier@trillion01.com>
Cc:     Jens Axboe <axboe@kernel.dk>, Stefan Metzmacher <metze@samba.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andy Lutomirski <luto@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        io-uring <io-uring@vger.kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Tue, May 11, 2021 at 9:24 PM Olivier Langlois <olivier@trillion01.com> wrote:
>
> I have reported an issue that I have with a user process using io_uring
> where when it core dumps, the dump fails to be generated.
> https://github.com/axboe/liburing/issues/346

I suspect most kernel developers don't have github notifications
enabled. I know I have them disabled because it would be *way* too
noisy not to.

But maybe Jens does for that libiouring part.

> Pavel did comment to my report and he did point out this thread as
> possibly a related issue.

I don't think this is related. The gdb confusion wouldn't affect core
dump generation.

I don't see why a core-dump shouldn't work from an IO thread these
days - the signal struct and synchronization should all be the same as
for a regular user thread.

That said, I do wonder if we should avoid generating core dumps from
the IO worker thread itself. The IO thread itself should never get a
SIGSEGV/SIGBUS anyway, it should have been turned into -EFAULT.

So maybe the

                if (current->flags & PF_IO_WORKER)
                        goto out;

in kernel/signal.c should be moved up above the do_coredump() logic regardless.

Jens, have you played with core-dumping when there are active io_uring
threads? There's a test-program in that github issue report..

              Linus