From: Al Viro <viro@ZenIV.linux.org.uk>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] fs: don't scan the inode cache before SB_ACTIVE is set
Date: Mon, 26 Mar 2018 06:31:51 +0100 [thread overview]
Message-ID: <20180326053151.GO30522@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20180326043503.17828-1-david@fromorbit.com>
On Mon, Mar 26, 2018 at 03:35:03PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> We recently had an oops reported on a 4.14 kernel in
> xfs_reclaim_inodes_count() where sb->s_fs_info pointed to garbage
> and so the m_perag_tree lookup walked into lala land.
>
> We found a mount in a failed state, blocked on teh shrinker rwsem
> here:
>
> mount_bdev()
> deactivate_locked_super()
> unregister_shrinker()
>
> Essentially, the machine was under memory pressure when the mount
> was being run, xfs_fs_fill_super() failed after allocating the
> xfs_mount and attaching it to sb->s_fs_info. It then cleaned up and
> freed the xfs_mount, but the sb->s_fs_info field still pointed to
> the freed memory. Hence when the superblock shrinker then ran
> it fell off the bad pointer.
>
> This is reproduced by using the mount_delay sysfs control as added
> in teh previous patch. It produces an oops down this path during the
> stalled mount:
> The problem is that the superblock shrinker is running before the
> filesystem structures it depends on have been fully set up. i.e.
> the shrinker is registered in sget(), before ->fill_super() has been
> called, and the shrinker can call into the filesystem before
> fill_super() does it's setup work.
Wait a sec... How the hell does it get through trylock_super() before
->s_root is set and ->s_umount is unlocked?
next prev parent reply other threads:[~2018-03-26 5:31 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-26 4:35 [PATCH] fs: don't scan the inode cache before SB_ACTIVE is set Dave Chinner
2018-03-26 5:31 ` Al Viro [this message]
2018-03-26 5:51 ` Al Viro
2018-03-26 6:33 ` Dave Chinner
2018-03-26 6:55 ` Al Viro
2018-03-26 7:21 ` Dave Chinner
2018-03-27 6:57 ` [PATCH V2] fs: don't scan the inode cache before SB_BORN " Dave Chinner
2018-03-27 7:24 ` Al Viro
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