From: Jens Axboe <axboe@kernel.dk>
To: Kent Overstreet <kent.overstreet@linux.dev>
Cc: torvalds@linux-foundation.org, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-bcachefs@vger.kernel.org,
Christoph Hellwig <hch@lst.de>,
Christian Brauner <brauner@kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [GIT PULL] bcachefs
Date: Wed, 28 Jun 2023 17:14:09 -0600 [thread overview]
Message-ID: <1e2134f1-f48b-1459-a38e-eac9597cd64a@kernel.dk> (raw)
In-Reply-To: <20230628225514.n3xtlgmjkgapgnrd@moria.home.lan>
On 6/28/23 4:55?PM, Kent Overstreet wrote:
>> But it's not aio (or io_uring or whatever), it's simply the fact that
>> doing an fput() from an exiting task (for example) will end up being
>> done async. And hence waiting for task exits is NOT enough to ensure
>> that all file references have been released.
>>
>> Since there are a variety of other reasons why a mount may be pinned and
>> fail to umount, perhaps it's worth considering that changing this
>> behavior won't buy us that much. Especially since it's been around for
>> more than 10 years:
>
> Because it seems that before io_uring the race was quite a bit harder to
> hit - I only started seeing it when things started switching over to
> io_uring. generic/388 used to pass reliably for me (pre backpointers),
> now it doesn't.
I literally just pasted a script that hits it in one second with aio. So
maybe generic/388 doesn't hit it as easily, but it's surely TRIVIAL to
hit with aio. As demonstrated. The io_uring is not hard to bring into
parity on that front, here's one I posted earlier today for 6.5:
https://lore.kernel.org/io-uring/20230628170953.952923-4-axboe@kernel.dk/
Doesn't change the fact that you can easily hit this with io_uring or
aio, and probably more things too (didn't look any further). Is it a
realistic thing outside of funky tests? Probably not really, or at least
if those guys hit it they'd probably have the work-around hack in place
in their script already.
But the fact is that it's been around for a decade. It's somehow a lot
easier to hit with bcachefs than XFS, which may just be because the
former has a bunch of workers and this may be deferring the delayed fput
work more. Just hand waving.
>> then we'd probably want to move that deferred fput list to the
>> task_struct and ensure that it gets run if the task exits rather than
>> have a global deferred list. Currently we have:
>>
>>
>> 1) If kthread or in interrupt
>> 1a) add to global fput list
>> 2) task_work_add if not. If that fails, goto 1a.
>>
>> which would then become:
>>
>> 1) If kthread or in interrupt
>> 1a) add to global fput list
>> 2) task_work_add if not. If that fails, we know task is existing. add to
>> per-task defer list to be run at a convenient time before task has
>> exited.
>
> no, it becomes:
> if we're running in a user task, or if we're doing an operation on
> behalf of a user task, add to the user task's deferred list: otherwise
> add to global deferred list.
And how would the "on behalf of a user task" work in terms of being
in_interrupt()?
--
Jens Axboe
next prev parent reply other threads:[~2023-06-28 23:14 UTC|newest]
Thread overview: 140+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-26 21:46 [GIT PULL] bcachefs Kent Overstreet
2023-06-26 23:11 ` Jens Axboe
2023-06-27 0:06 ` Kent Overstreet
2023-06-27 1:13 ` Jens Axboe
2023-06-27 2:05 ` Kent Overstreet
2023-06-27 2:59 ` Jens Axboe
2023-06-27 3:10 ` Kent Overstreet
2023-06-27 17:16 ` Jens Axboe
2023-06-27 20:15 ` Kent Overstreet
2023-06-27 22:05 ` Dave Chinner
2023-06-27 22:41 ` Kent Overstreet
2023-06-28 14:40 ` Jens Axboe
2023-06-28 14:48 ` Thomas Weißschuh
2023-06-28 14:58 ` Jens Axboe
2023-06-28 3:16 ` Jens Axboe
2023-06-28 4:01 ` Kent Overstreet
2023-06-28 14:58 ` Jens Axboe
2023-06-28 15:22 ` Jens Axboe
2023-06-28 17:56 ` Kent Overstreet
2023-06-28 20:45 ` Jens Axboe
2023-06-28 16:57 ` Jens Axboe
2023-06-28 17:33 ` Christian Brauner
2023-06-28 17:52 ` Kent Overstreet
2023-06-28 20:44 ` Jens Axboe
2023-06-28 21:17 ` Jens Axboe
2023-06-28 22:13 ` Kent Overstreet
2023-06-28 22:33 ` Jens Axboe
2023-06-28 22:55 ` Kent Overstreet
2023-06-28 23:14 ` Jens Axboe [this message]
2023-06-28 23:50 ` Kent Overstreet
2023-06-29 1:00 ` Dave Chinner
2023-06-29 1:33 ` Jens Axboe
2023-06-29 11:18 ` Christian Brauner
2023-06-29 14:17 ` Kent Overstreet
2023-06-29 15:31 ` Kent Overstreet
2023-06-30 9:40 ` Christian Brauner
2023-07-06 15:20 ` Kent Overstreet
2023-07-06 16:26 ` Jens Axboe
2023-07-06 16:34 ` Kent Overstreet
2023-06-29 1:29 ` Jens Axboe
2023-07-06 20:15 ` Kent Overstreet
2023-06-28 17:54 ` Kent Overstreet
2023-06-28 20:54 ` Jens Axboe
2023-06-28 22:14 ` Jens Axboe
2023-06-28 23:04 ` Kent Overstreet
2023-06-28 23:11 ` Jens Axboe
2023-06-27 2:33 ` Kent Overstreet
2023-06-27 2:59 ` Jens Axboe
2023-06-27 3:19 ` Matthew Wilcox
2023-06-27 3:22 ` Kent Overstreet
2023-06-27 3:52 ` Christoph Hellwig
2023-06-27 4:36 ` Kent Overstreet
2023-07-06 15:56 ` Kent Overstreet
2023-07-06 16:40 ` Josef Bacik
2023-07-06 17:38 ` Kent Overstreet
2023-07-06 19:17 ` Eric Sandeen
2023-07-06 19:31 ` Kent Overstreet
2023-07-06 21:19 ` Darrick J. Wong
2023-07-06 22:43 ` Kent Overstreet
2023-07-07 13:13 ` Jan Kara
2023-07-07 13:52 ` Kent Overstreet
2023-07-07 8:48 ` Christian Brauner
2023-07-07 9:18 ` Kent Overstreet
2023-07-07 16:26 ` James Bottomley
2023-07-07 16:48 ` Kent Overstreet
2023-07-07 17:04 ` James Bottomley
2023-07-07 17:26 ` Kent Overstreet
2023-07-08 3:54 ` Matthew Wilcox
2023-07-08 4:10 ` Kent Overstreet
2023-07-08 4:31 ` Kent Overstreet
2023-07-08 15:02 ` Theodore Ts'o
2023-07-08 15:23 ` Kent Overstreet
2023-07-08 16:42 ` James Bottomley
2023-07-09 1:16 ` Kent Overstreet
2023-07-07 9:35 ` Kent Overstreet
2023-07-07 2:04 ` Theodore Ts'o
2023-07-07 12:18 ` Brian Foster
2023-07-07 14:49 ` Kent Overstreet
2023-07-12 2:54 ` Kent Overstreet
2023-07-12 19:48 ` Kees Cook
2023-07-12 19:57 ` Kent Overstreet
2023-07-12 22:10 ` Darrick J. Wong
2023-07-12 23:57 ` Kent Overstreet
2023-08-09 1:27 ` Linus Torvalds
2023-08-10 15:54 ` Kent Overstreet
2023-08-10 16:40 ` Linus Torvalds
2023-08-10 18:02 ` Kent Overstreet
2023-08-10 18:09 ` Linus Torvalds
2023-08-10 17:52 ` Jan Kara
2023-08-11 2:47 ` Kent Overstreet
2023-08-11 8:10 ` Jan Kara
2023-08-11 8:13 ` Christian Brauner
2023-08-10 22:39 ` Darrick J. Wong
2023-08-10 23:47 ` Linus Torvalds
2023-08-11 2:40 ` Jens Axboe
2023-08-11 4:03 ` Kent Overstreet
2023-08-11 5:20 ` Linus Torvalds
2023-08-11 5:29 ` Kent Overstreet
2023-08-11 5:53 ` Linus Torvalds
2023-08-11 7:52 ` Christian Brauner
2023-08-11 14:31 ` Jens Axboe
2023-08-11 3:45 ` Kent Overstreet
2023-08-21 0:09 ` Dave Chinner
2023-08-10 23:07 ` Matthew Wilcox
2023-08-11 10:54 ` Christian Brauner
2023-08-11 12:58 ` Kent Overstreet
2023-08-14 7:25 ` Christian Brauner
2023-08-14 15:23 ` Kent Overstreet
2023-08-11 13:21 ` Kent Overstreet
2023-08-11 22:56 ` Darrick J. Wong
2023-08-14 7:21 ` Christian Brauner
2023-08-14 15:27 ` Kent Overstreet
2023-09-03 3:25 Kent Overstreet
2023-09-05 13:24 ` Christoph Hellwig
2023-09-06 0:00 ` Kent Overstreet
2023-09-06 0:41 ` Matthew Wilcox
2023-09-06 16:10 ` Kent Overstreet
2023-09-06 17:57 ` Darrick J. Wong
2023-09-08 9:37 ` Christoph Hellwig
2023-09-06 19:36 ` Linus Torvalds
2023-09-06 20:02 ` Linus Torvalds
2023-09-06 20:20 ` Linus Torvalds
2023-09-06 21:55 ` Arnaldo Carvalho de Melo
2023-09-06 23:13 ` David Sterba
2023-09-06 23:34 ` Linus Torvalds
2023-09-06 23:46 ` Arnaldo Carvalho de Melo
2023-09-06 23:53 ` Arnaldo Carvalho de Melo
2023-09-06 23:16 ` Linus Torvalds
2023-09-10 0:53 ` Kent Overstreet
2023-09-07 20:37 ` Kent Overstreet
2023-09-07 20:51 ` Linus Torvalds
2023-09-07 23:40 ` Kent Overstreet
2023-09-08 6:29 ` Martin Steigerwald
2023-09-08 9:11 ` Joshua Ashton
2023-09-06 22:28 ` Nathan Chancellor
2023-09-07 0:03 ` Kees Cook
2023-09-07 14:29 ` Chris Mason
2023-09-07 20:39 ` Kent Overstreet
2023-09-08 10:50 ` Brian Foster
2023-09-08 23:05 ` Dave Chinner
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