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From: Jann Horn <jannh@google.com>
To: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
	raven@themaw.net, Miklos Szeredi <mszeredi@redhat.com>,
	Christian Brauner <christian@brauner.io>,
	Linux API <linux-api@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	kernel list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 15/19] vfs: Add superblock notifications [ver #16]
Date: Fri, 21 Feb 2020 17:41:31 +0100	[thread overview]
Message-ID: <CAG48ez2vzgVgJw7-WKa1GbyLw2nJGvAnS21w=gHV02rUNheYFw@mail.gmail.com> (raw)
In-Reply-To: <2031798.1582302800@warthog.procyon.org.uk>

On Fri, Feb 21, 2020 at 5:33 PM David Howells <dhowells@redhat.com> wrote:
> Jann Horn <jannh@google.com> wrote:
>
> > (And as in the other case, the s->s_count increment will probably have
> > to be moved above the add_watch_to_object(), unless you hold the
> > sb_lock around it?)
>
> It shouldn't matter as I'm holding s->s_umount across the add and increment.
> That prevents the watch from being removed: watch_sb() would have to get the
> lock first to do that.  It also deactivate_locked_super() from removing all
> the watchers.

Can't the same thing I already pointed out on "[PATCH 13/19] vfs: Add
a mount-notification facility [ver #16]" also happen here?

If another thread concurrently runs close(watch_fd) before the
spin_lock(&sb_lock), pipe_release -> put_pipe_info -> free_pipe_info
-> watch_queue_clear will run, correct? And then watch_queue_clear()
will find the watch that we've just created and call its
->release_watch() handler, which causes put_super(), potentially
dropping the refcount to zero? And then stuff will blow up.

> I can move it before, but I probably have to drop s_umount before I can call
> put_super().

  reply	other threads:[~2020-02-21 16:42 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-18 17:04 [PATCH 00/19] VFS: Filesystem information and notifications [ver #16] David Howells
2020-02-18 17:05 ` [PATCH 01/19] vfs: syscall: Add fsinfo() to query filesystem information " David Howells
2020-02-19 16:31   ` Darrick J. Wong
2020-02-19 20:07   ` Jann Horn
2020-02-20 10:34   ` David Howells
2020-02-20 15:48     ` Darrick J. Wong
2020-02-20 11:03   ` David Howells
2020-02-20 14:54     ` Jann Horn
2020-02-20 15:31       ` Darrick J. Wong
2020-02-18 17:05 ` [PATCH 02/19] fsinfo: Add syscalls to other arches " David Howells
2020-02-21 14:51   ` Christian Brauner
2020-02-21 18:10     ` Geert Uytterhoeven
2020-02-18 17:05 ` [PATCH 03/19] fsinfo: Provide a bitmap of supported features " David Howells
2020-02-19 16:37   ` Darrick J. Wong
2020-02-20 12:22   ` David Howells
2020-02-18 17:05 ` [PATCH 04/19] vfs: Add mount change counter " David Howells
2020-02-21 14:48   ` Christian Brauner
2020-02-18 17:05 ` [PATCH 05/19] vfs: Introduce a non-repeating system-unique superblock ID " David Howells
2020-02-19 16:53   ` Darrick J. Wong
2020-02-20 12:45   ` David Howells
2020-02-18 17:05 ` [PATCH 06/19] vfs: Allow fsinfo() to look up a mount object by " David Howells
2020-02-21 15:09   ` Christian Brauner
2020-02-18 17:05 ` [PATCH 07/19] vfs: Allow mount information to be queried by fsinfo() " David Howells
2020-02-18 17:05 ` [PATCH 08/19] vfs: fsinfo sample: Mount listing program " David Howells
2020-02-18 17:06 ` [PATCH 09/19] fsinfo: Allow the mount topology propogation flags to be retrieved " David Howells
2020-02-18 17:06 ` [PATCH 10/19] fsinfo: Add API documentation " David Howells
2020-02-18 17:06 ` [PATCH 11/19] afs: Support fsinfo() " David Howells
2020-02-19 21:01   ` Jann Horn
2020-02-20 12:58   ` David Howells
2020-02-20 14:58     ` Jann Horn
2020-02-21 13:26     ` David Howells
2020-02-18 17:06 ` [PATCH 12/19] security: Add hooks to rule on setting a superblock or mount watch " David Howells
2020-02-18 17:06 ` [PATCH 13/19] vfs: Add a mount-notification facility " David Howells
2020-02-19 22:40   ` Jann Horn
2020-02-19 22:55     ` Jann Horn
2020-02-21 12:24   ` David Howells
2020-02-21 15:49     ` Jann Horn
2020-02-21 17:06     ` David Howells
2020-02-21 17:36       ` seq_lock and lockdep_is_held() assertions Jann Horn
2020-02-21 18:02         ` John Stultz
2020-02-18 17:06 ` [PATCH 14/19] notifications: sample: Display mount tree change notifications [ver #16] David Howells
2020-02-18 17:06 ` [PATCH 15/19] vfs: Add superblock " David Howells
2020-02-19 23:08   ` Jann Horn
2020-02-21 14:23   ` David Howells
2020-02-21 15:44     ` Jann Horn
2020-02-21 16:33     ` David Howells
2020-02-21 16:41       ` Jann Horn [this message]
2020-02-21 17:11       ` David Howells
2020-02-18 17:06 ` [PATCH 16/19] fsinfo: Provide superblock notification counter " David Howells
2020-02-18 17:07 ` [PATCH 17/19] notifications: sample: Display superblock notifications " David Howells
2020-02-18 17:07 ` [PATCH 18/19] ext4: Add example fsinfo information " David Howells
2020-02-19 17:04   ` Darrick J. Wong
2020-02-20  0:53   ` kbuild test robot
2020-02-21 14:43   ` David Howells
2020-02-21 16:26     ` Darrick J. Wong
2020-02-18 17:07 ` [PATCH 19/19] nfs: Add example filesystem " David Howells
2020-02-20  2:13   ` kbuild test robot
2020-02-20  2:20   ` kbuild test robot
2020-02-18 18:12 ` David Howells
2020-02-19 10:23 ` [PATCH 00/19] VFS: Filesystem information and notifications " Stefan Metzmacher
2020-02-19 14:46 ` Christian Brauner
2020-02-19 15:50   ` Darrick J. Wong
2020-02-20  4:42   ` Ian Kent
2020-02-20  9:09     ` Christian Brauner
2020-02-20 11:30       ` Ian Kent
2020-02-19 16:16 ` David Howells
2020-02-21 12:57 ` David Howells

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