Re: [PATCH v2] Btrfs: fix missing delayed iputs on unmount

[Omar Sandoval <osandov@osandov.com>]

On Wed, Nov 07, 2018 at 05:01:19PM +0100, David Sterba wrote:
> On Wed, Oct 31, 2018 at 10:06:08AM -0700, Omar Sandoval wrote:
> > From: Omar Sandoval <osandov@fb.com>
> > 
> > There's a race between close_ctree() and cleaner_kthread().
> > close_ctree() sets btrfs_fs_closing(), and the cleaner stops when it
> > sees it set, but this is racy; the cleaner might have already checked
> > the bit and could be cleaning stuff. In particular, if it deletes unused
> > block groups, it will create delayed iputs for the free space cache
> > inodes. As of "btrfs: don't run delayed_iputs in commit", we're no
> > longer running delayed iputs after a commit. Therefore, if the cleaner
> > creates more delayed iputs after delayed iputs are run in
> > btrfs_commit_super(), we will leak inodes on unmount and get a busy
> > inode crash from the VFS.
> > 
> > Fix it by parking the cleaner before we actually close anything. Then,
> > any remaining delayed iputs will always be handled in
> > btrfs_commit_super(). This also ensures that the commit in close_ctree()
> > is really the last commit, so we can get rid of the commit in
> > cleaner_kthread().
> > 
> > Fixes: 30928e9baac2 ("btrfs: don't run delayed_iputs in commit")
> > Signed-off-by: Omar Sandoval <osandov@fb.com>
> 
> I'll queue this patch for rc2 as it fixes crashes I see during testing.
> My version does more changes and would be more suitable for a series,
> that could actually document the shutdown sequence and add a few
> assertions on top.

Thanks, Dave! I'll keep an eye out for the further cleanups.

> Reviewed-by: David Sterba <dsterba@suse.com>