On Mon 02-05-11 09:22:04, Christoph Hellwig wrote:
> On Mon, May 02, 2011 at 03:16:19PM +0200, Jan Kara wrote:
> > Dave, Christoph, any opinions on this?
>
> The busyloop in xfs_quiesce_attr which waits for all active transactions
> to finish is supposed to fix this issue.
Hmm, but what prevents the following race?
Thread 1 Thread 2
..
xfs_trans_alloc()
xfs_wait_for_freeze(mp, SB_FREEZE_TRANS);
freeze_super()
...
xfs_fs_freeze()
...
xfs_quiesce_attr()
...
_xfs_trans_alloc()
atomic_inc(&mp->m_active_trans);
... goes on modifying the filesystem
It seems to be a similar problem as in ext4 - the atomic_inc() and
vfs_check_frozen() are in the wrong order...
> Note that XFS traditionally expects a two stage freeze process where
> we first freeze new VFS-level writes, then flush the caches and then
> stop transactions, wait for them to finish and do the remainder of
> the freeze process, but I really messed that process up when moving
> the sequence to generic code. Funnily enough it seems to work
> neverless.
Honza
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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