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From: Olivier Langlois <olivier@trillion01.com>
To: Pavel Begunkov <asml.silence@gmail.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	linux-kernel@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Jens Axboe <axboe@kernel.dk>, Oleg Nesterov <oleg@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [RFC] coredump: Do not interrupt dump for TIF_NOTIFY_SIGNAL
Date: Thu, 23 Dec 2021 20:34:54 -0500	[thread overview]
Message-ID: <b3e43e07c68696b83a5bf25664a3fa912ba747e2.camel@trillion01.com> (raw)
In-Reply-To: <1b519092-2ebf-3800-306d-c354c24a9ad1@gmail.com>

On Fri, 2021-10-22 at 15:13 +0100, Pavel Begunkov wrote:
> On 6/9/21 21:17, Eric W. Biederman wrote:
> > 
> > Folks,
> > 
> > Olivier Langlois has been struggling with coredumps getting
> > truncated in
> > tasks using io_uring.  He has also apparently been struggling with
> > the some of his email messages not making it to the lists.
> 
> Looks syzbot hit something relevant, see
> https://lore.kernel.org/io-
> uring/0000000000000012fb05cee99477@google.com/
> 
> In short, a task creates an io_uring worker thread, then the worker
> submits a task_work item to the creator task and won't die until
> the item is executed/cancelled. And I found that the creator task is
> sleeping in do_coredump() -> wait_for_completion()
> 
> 0xffffffff81343ccb is in do_coredump (fs/coredump.c:469).
> 464
> 465             if (core_waiters > 0) {
> 466                     struct core_thread *ptr;
> 467
> 468                     freezer_do_not_count();
> 469                     wait_for_completion(&core_state->startup);
> 470                     freezer_count();
> 
> 
> A hack executing tws there helps (see diff below).
> Any chance anyone knows what this is and how to fix it?
> 
> 
> diff --git a/fs/coredump.c b/fs/coredump.c
> index 3224dee44d30..f6f9dfb02296 100644
> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -466,7 +466,8 @@ static int coredump_wait(int exit_code, struct
> core_state *core_state)
>           struct core_thread *ptr;
>   
>           freezer_do_not_count();
> -        wait_for_completion(&core_state->startup);
> +        while (wait_for_completion_interruptible(&core_state-
> >startup))
> +            tracehook_notify_signal();
>           freezer_count();
>           /*
>            * Wait for all the threads to become inactive, so that
> 
> 
> 
> 
Pavel,

I cannot comment on the merit of the proposed hack but my proposed
patch to fix the coredump truncation issue when a process using
io_uring core dumps that I submitted back in August is still
unreviewed!

https://lore.kernel.org/lkml/1625bc89782bf83d9d8c7c63e8ffcb651ccb15fa.1629655338.git.olivier@trillion01.com/

I have been using it since then I must have generated many dozens of
perfect core dump files with it and I have not seen a single truncated
core dump files like I used to have prior to the patch.

I am bringing back my patch to your attention because one nice side
effect of it is that it would have avoided totally the problem that you
have encountered in coredump_wait() since it does cancel io_uring
resources before calling coredump_wait()!

Greetings,
Olivier


  reply	other threads:[~2021-12-24  1:35 UTC|newest]

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <192c9697e379bf084636a8213108be6c3b948d0b.camel@trillion01.com>
     [not found] ` <9692dbb420eef43a9775f425cb8f6f33c9ba2db9.camel@trillion01.com>
     [not found]   ` <87h7i694ij.fsf_-_@disp2133>
2021-06-09 20:33     ` [RFC] coredump: Do not interrupt dump for TIF_NOTIFY_SIGNAL Linus Torvalds
2021-06-09 20:48       ` Eric W. Biederman
2021-06-09 20:52         ` Linus Torvalds
2021-06-09 21:02       ` Olivier Langlois
2021-06-09 21:05         ` Eric W. Biederman
2021-06-09 21:26           ` Olivier Langlois
2021-06-09 21:56             ` Olivier Langlois
2021-06-10 14:26             ` Eric W. Biederman
2021-06-10 15:17               ` Olivier Langlois
2021-06-10 18:58               ` [CFT}[PATCH] coredump: Limit what can interrupt coredumps Eric W. Biederman
2021-06-10 19:10                 ` Linus Torvalds
2021-06-10 19:18                   ` Eric W. Biederman
2021-06-10 19:50                     ` Linus Torvalds
2021-06-10 20:11                       ` [PATCH] " Eric W. Biederman
2021-06-10 21:04                         ` Linus Torvalds
2021-06-12 14:36                         ` Olivier Langlois
2021-06-12 16:26                           ` Jens Axboe
2021-06-14 14:10                         ` Oleg Nesterov
2021-06-14 16:37                           ` Eric W. Biederman
2021-06-14 16:59                             ` Oleg Nesterov
2021-06-15 22:08                           ` Eric W. Biederman
2021-06-16 19:23                             ` Olivier Langlois
2021-06-16 20:00                               ` Eric W. Biederman
2021-06-18 20:05                                 ` Olivier Langlois
2021-08-05 13:06                             ` Olivier Langlois
2021-08-10 21:48                               ` Tony Battersby
2021-08-11 20:47                                 ` Olivier Langlois
2021-08-12  1:55                                 ` Jens Axboe
2021-08-12 13:53                                   ` Tony Battersby
2021-08-15 20:42                                   ` Olivier Langlois
2021-08-16 13:02                                     ` Pavel Begunkov
2021-08-16 13:06                                       ` Pavel Begunkov
2021-08-17 18:15                                     ` Jens Axboe
2021-08-17 18:24                                       ` Jens Axboe
2021-08-17 19:29                                         ` Tony Battersby
2021-08-17 19:59                                           ` Jens Axboe
2021-08-17 21:28                                             ` Jens Axboe
2021-08-17 21:39                                               ` Tony Battersby
2021-08-17 22:05                                                 ` Jens Axboe
2021-08-18 14:37                                                   ` Tony Battersby
2021-08-18 14:46                                                     ` Jens Axboe
2021-08-18  2:57                                               ` Jens Axboe
2021-08-18  2:58                                                 ` Jens Axboe
2021-08-21 10:08                                                 ` Olivier Langlois
2021-08-21 16:47                                                   ` Olivier Langlois
2021-08-21 16:51                                                     ` Jens Axboe
2021-08-21 17:21                                                       ` Olivier Langlois
2021-08-21  9:52                                         ` Olivier Langlois
2021-08-21  9:48                                       ` Olivier Langlois
2021-10-22 14:13     ` [RFC] coredump: Do not interrupt dump for TIF_NOTIFY_SIGNAL Pavel Begunkov
2021-12-24  1:34       ` Olivier Langlois [this message]
2021-12-24 10:37         ` Pavel Begunkov
2021-12-24 19:52           ` Eric W. Biederman
2021-12-28 11:24             ` Pavel Begunkov
2022-03-14 23:58               ` Eric W. Biederman
     [not found]                 ` <8218f1a245d054c940e25142fd00a5f17238d078.camel@trillion01.com>
2022-06-01  3:15                   ` Jens Axboe
2022-07-20 16:49                     ` [PATCH 0/2] coredump: Allow io_uring using apps to dump to pipes Eric W. Biederman
2022-07-20 16:50                       ` [PATCH 1/2] signal: Move stopping for the coredump from do_exit into get_signal Eric W. Biederman
2022-07-20 16:51                       ` [PATCH 2/2] coredump: Allow coredumps to pipes to work with io_uring Eric W. Biederman
2022-08-22 21:16                         ` Olivier Langlois
2022-08-23  3:35                           ` Olivier Langlois
2022-08-23 18:22                             ` Eric W. Biederman
2022-08-23 18:27                               ` Jens Axboe
2022-08-24 15:11                                 ` Eric W. Biederman
2022-08-24 15:51                                   ` Jens Axboe
2022-01-05 19:39           ` [RFC] coredump: Do not interrupt dump for TIF_NOTIFY_SIGNAL Olivier Langlois

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