From: [email protected] (Eric W. Biederman)
To: Oleg Nesterov <[email protected]>
Cc: Linus Torvalds <[email protected]>,
Olivier Langlois <[email protected]>,
Linux Kernel Mailing List <[email protected]>,
linux-fsdevel <[email protected]>,
io-uring <[email protected]>,
Alexander Viro <[email protected]>,
Jens Axboe <[email protected]>,
"Pavel Begunkov\>" <[email protected]>
Subject: Re: [PATCH] coredump: Limit what can interrupt coredumps
Date: Tue, 15 Jun 2021 17:08:23 -0500 [thread overview]
Message-ID: <87pmwmn5m0.fsf@disp2133> (raw)
In-Reply-To: <[email protected]> (Oleg Nesterov's message of "Mon, 14 Jun 2021 16:10:33 +0200")
Oleg Nesterov <[email protected]> writes:
>> --- a/fs/coredump.c
>> +++ b/fs/coredump.c
>> @@ -519,7 +519,7 @@ static bool dump_interrupted(void)
>> * but then we need to teach dump_write() to restart and clear
>> * TIF_SIGPENDING.
>> */
>> - return signal_pending(current);
>> + return fatal_signal_pending(current) || freezing(current);
>> }
>
>
> Well yes, this is what the comment says.
>
> But note that there is another reason why dump_interrupted() returns true
> if signal_pending(), it assumes thagt __dump_emit()->__kernel_write() may
> fail anyway if signal_pending() is true. Say, pipe_write(), or iirc nfs,
> perhaps something else...
>
> That is why zap_threads() clears TIF_SIGPENDING. Perhaps it should clear
> TIF_NOTIFY_SIGNAL as well and we should change io-uring to not abuse the
> dumping threads?
>
> Or perhaps we should change __dump_emit() to clear signal_pending() and
> restart __kernel_write() if it fails or returns a short write.
>
> Otherwise the change above doesn't look like a full fix to me.
Agreed. The coredump to a pipe will still be short. That needs
something additional.
The problem Olivier Langlois <[email protected]> reported was
core dumps coming up short because TIF_NOTIFY_SIGNAL was being
set during a core dump.
We can see this with pipe_write returning -ERESTARTSYS
on a full pipe if signal_pending which includes TIF_NOTIFY_SIGNAL
is true.
Looking further if the thread that is core dumping initiated
any io_uring work then io_ring_exit_work will use task_work_add
to request that thread clean up it's io_uring state.
Perhaps we can put a big comment in dump_emit and if we
get back -ERESTARTSYS run tracework_notify_signal. I am not
seeing any locks held at that point in the coredump, so it
should be safe. The coredump is run inside of file_start_write
which is the only potential complication.
The code flow is complicated but it looks like the entire
point of the exercise is to call io_uring_del_task_file
on the originating thread. I suppose that keeps the
locking of the xarray in io_uring_task simple.
Hmm. All of this comes from io_uring_release.
How do we get to io_uring_release? The coredump should
be catching everything in exit_mm before exit_files?
Confused and hopeful someone can explain to me what is going on,
and perhaps simplify it.
Eric
next prev parent reply other threads:[~2021-06-15 22:09 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <[email protected]>
[not found] ` <[email protected]>
[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 [this message]
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
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] ` <[email protected]>
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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