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From: Tycho Andersen <tycho@tycho.pizza>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Eric Biederman <ebiederm@xmission.com>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	linux-kernel@vger.kernel.org, fuse-devel@lists.sourceforge.net
Subject: Re: [PATCH v2] fuse: In fuse_flush only wait if someone wants the return code
Date: Fri, 30 Sep 2022 10:09:56 -0600	[thread overview]
Message-ID: <YzcU1IhHEa2oV0vo@tycho.pizza> (raw)
In-Reply-To: <CAJfpegsZk+R2wmXo_358J6YrxLaWN7=VAUEUaGjF1Jveb+qKJQ@mail.gmail.com>

On Fri, Sep 30, 2022 at 04:41:37PM +0200, Miklos Szeredi wrote:
> On Fri, 30 Sept 2022 at 16:01, Tycho Andersen <tycho@tycho.pizza> wrote:
> >
> > On Fri, Sep 30, 2022 at 03:35:16PM +0200, Miklos Szeredi wrote:
> > > On Thu, 29 Sept 2022 at 18:40, Tycho Andersen <tycho@tycho.pizza> wrote:
> > > >
> > > > If a fuse filesystem is mounted inside a container, there is a problem
> > > > during pid namespace destruction. The scenario is:
> > > >
> > > > 1. task (a thread in the fuse server, with a fuse file open) starts
> > > >    exiting, does exit_signals(), goes into fuse_flush() -> wait
> > >
> > > Can't the same happen through
> > >
> > >   fuse_flush -> fuse_sync_writes -> fuse_set_nowrite -> wait
> > >
> > > ?
> >
> > Looks like yes, though I haven't seen this in the wild, I guess
> > because there aren't multiple writers most of the time the user code
> > that causes this.
> >
> > I'm not exactly sure how to fix this. Reading through 3be5a52b30aa
> > ("fuse: support writable mmap"), we don't want to allow multiple
> > writes since that may do allocations, which could cause deadlocks. But
> > in this case we have no reliable way to wait (besides a busy loop, I
> > suppose).
> >
> > Maybe just a check for PF_EXITING and a pr_warn() with "echo 1 >
> > /sys/fs/fuse/connections/$N/abort" or something?
> 
> AFAICS it should be perfectly normal (and trivial to trigger) for an
> exiting process to have its dirty pages flushed through fuse_flush().

Agreed.

> We could do that asynchronously as well, generally there are no
> promises about dirty pages being synced as part of the process exiting
> .  But ordering between dirty page flushing and sending the FUSE_FLUSH
> request should be kept.  Which needs more complexity, unfortunately.

How can we wait in fuse_set_nowrite()? Or are you suggesting we just
do a fuse_flush_writepages() in the async part and hope for the best?

Thanks,

Tycho

  reply	other threads:[~2022-09-30 16:10 UTC|newest]

Thread overview: 61+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-23 17:21 strange interaction between fuse + pidns Tycho Andersen
2022-06-23 21:55 ` Vivek Goyal
2022-06-23 23:41   ` Tycho Andersen
2022-06-24 17:36     ` Vivek Goyal
2022-07-11 10:35 ` Miklos Szeredi
2022-07-11 13:59   ` Miklos Szeredi
2022-07-11 20:25     ` Tycho Andersen
2022-07-11 21:37       ` Eric W. Biederman
2022-07-11 22:53         ` Tycho Andersen
2022-07-11 23:06           ` Eric W. Biederman
2022-07-12 13:43             ` Tycho Andersen
2022-07-12 14:34               ` Eric W. Biederman
2022-07-12 15:14                 ` Tycho Andersen
2022-07-13 17:53                   ` [PATCH] sched: __fatal_signal_pending() should also check PF_EXITING Tycho Andersen
2022-07-20 15:03                     ` Serge E. Hallyn
2022-07-20 20:58                       ` Tycho Andersen
2022-07-21  1:54                         ` Serge E. Hallyn
2022-07-27 15:44                           ` Tycho Andersen
2022-07-27 16:32                             ` Eric W. Biederman
2022-07-27 17:55                               ` Tycho Andersen
2022-07-28 18:48                                 ` Eric W. Biederman
2022-07-27 17:55                             ` Oleg Nesterov
2022-07-27 18:18                               ` Tycho Andersen
2022-07-27 19:19                                 ` Oleg Nesterov
2022-07-27 19:40                                   ` Tycho Andersen
2022-07-28  9:12                                     ` Oleg Nesterov
2022-07-28 21:20                                       ` Tycho Andersen
2022-07-29  5:04                                         ` Eric W. Biederman
2022-07-29 13:50                                           ` Tycho Andersen
2022-07-29 16:15                                             ` Eric W. Biederman
2022-07-29 16:48                                               ` Tycho Andersen
2022-07-29 17:40                                                 ` [RFC][PATCH] fuse: In fuse_flush only wait if someone wants the return code Eric W. Biederman
2022-07-29 20:47                                                   ` Oleg Nesterov
2022-07-30  0:15                                                     ` Al Viro
2022-07-30  5:10                                                       ` [RFC][PATCH v2] " Eric W. Biederman
2022-08-01 15:16                                                         ` Tycho Andersen
2022-08-02 12:50                                                         ` Miklos Szeredi
2022-08-15 13:59                                                         ` Tycho Andersen
2022-08-15 17:55                                                           ` Serge E. Hallyn
2022-09-01 14:06                                                           ` [PATCH] " Tycho Andersen
2022-09-19 15:03                                                             ` Tycho Andersen
2022-09-20 18:02                                                               ` Serge E. Hallyn
2022-09-26 14:17                                                               ` Tycho Andersen
2022-09-27  9:46                                                             ` Miklos Szeredi
2022-09-29 14:05                                                               ` [fuse-devel] " Stef Bon
2022-09-29 16:39                                                               ` [PATCH v2] " Tycho Andersen
2022-09-30 13:35                                                                 ` Miklos Szeredi
2022-09-30 14:01                                                                   ` Tycho Andersen
2022-09-30 14:41                                                                     ` Miklos Szeredi
2022-09-30 16:09                                                                       ` Tycho Andersen [this message]
2022-10-26  9:01                                                                         ` Miklos Szeredi
2022-11-14 16:02                                                                           ` [PATCH v3] " Tycho Andersen
2022-11-28 15:00                                                                             ` Tycho Andersen
2022-12-08 14:26                                                                               ` Miklos Szeredi
2022-12-08 17:49                                                                                 ` Tycho Andersen
2022-12-19 19:16                                                                                   ` Tycho Andersen
2023-01-03 14:51                                                                                     ` Tycho Andersen
2023-01-05 15:15                                                                                       ` Serge E. Hallyn
2023-01-26 14:12                                                                                       ` Miklos Szeredi
2022-09-30 19:47                                                               ` [PATCH] " Serge E. Hallyn
2022-09-19 15:46                                                           ` [RFC][PATCH v2] " Eric W. Biederman

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