From: Max Reitz <mreitz@redhat.com>
To: Greg Kurz <groug@kaod.org>, Miklos Szeredi <miklos@szeredi.hu>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
virtio-fs@redhat.com, Vivek Goyal <vgoyal@redhat.com>,
stable@vger.kernel.org
Subject: Re: [PATCH v2 3/7] fuse: Fix infinite loop in sget_fc()
Date: Tue, 8 Jun 2021 17:12:15 +0200 [thread overview]
Message-ID: <1fc488d8-91b8-9613-8127-a8b34ddb4744@redhat.com> (raw)
In-Reply-To: <20210604161156.408496-4-groug@kaod.org>
On 04.06.21 18:11, Greg Kurz wrote:
> We don't set the SB_BORN flag on submounts. This is wrong as these
> superblocks are then considered as partially constructed or dying
> in the rest of the code and can break some assumptions.
>
> One such case is when you have a virtiofs filesystem with submounts
> and you try to mount it again : virtio_fs_get_tree() tries to obtain
> a superblock with sget_fc(). The logic in sget_fc() is to loop until
> it has either found an existing matching superblock with SB_BORN set
> or to create a brand new one. It is assumed that a superblock without
> SB_BORN is transient and the loop is restarted. Forgetting to set
> SB_BORN on submounts hence causes sget_fc() to retry forever.
>
> Setting SB_BORN requires special care, i.e. a write barrier for
> super_cache_count() which can check SB_BORN without taking any lock.
> We should call vfs_get_tree() to deal with that but this requires
> to have a proper ->get_tree() implementation for submounts, which
> is a bigger piece of work. Go for a simple bug fix in the meatime.
>
> Fixes: bf109c64040f ("fuse: implement crossmounts")
> Cc: mreitz@redhat.com
> Cc: stable@vger.kernel.org # v5.10+
> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---
> fs/fuse/dir.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
Reviewed-by: Max Reitz <mreitz@redhat.com>
next prev parent reply other threads:[~2021-06-08 15:12 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-04 16:11 [PATCH v2 0/7] fuse: Some fixes for submounts Greg Kurz
2021-06-04 16:11 ` [PATCH v2 1/7] fuse: Fix crash in fuse_dentry_automount() error path Greg Kurz
2021-06-04 16:11 ` [PATCH v2 2/7] fuse: Fix crash if superblock of submount gets killed early Greg Kurz
2021-06-08 15:08 ` Max Reitz
2021-06-04 16:11 ` [PATCH v2 3/7] fuse: Fix infinite loop in sget_fc() Greg Kurz
2021-06-08 15:12 ` Max Reitz [this message]
2021-06-04 16:11 ` [PATCH v2 4/7] fuse: Add dedicated filesystem context ops for submounts Greg Kurz
2021-06-08 15:25 ` Max Reitz
2021-06-04 16:11 ` [PATCH v2 5/7] fuse: Call vfs_get_tree() " Greg Kurz
2021-06-08 15:40 ` Max Reitz
2021-06-04 16:11 ` [PATCH v2 6/7] fuse: Switch to fc_mount() " Greg Kurz
2021-06-08 15:51 ` Max Reitz
2021-06-09 7:45 ` Greg Kurz
2021-06-11 14:44 ` Miklos Szeredi
2021-06-04 16:11 ` [PATCH v2 7/7] fuse: Make fuse_fill_super_submount() static Greg Kurz
2021-06-08 15:52 ` [PATCH v2 0/7] fuse: Some fixes for submounts Max Reitz
2021-06-09 7:46 ` Greg Kurz
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