On Mon, May 02, 2011 at 04:20:55PM +0200, Jan Kara wrote:
> Hmm, but what prevents the following race?
>
> Thread 1 Thread 2
> ..
> xfs_trans_alloc()
> xfs_wait_for_freeze(mp, SB_FREEZE_TRANS);
> freeze_super()
sb->s_frozen = SB_FREEZE_TRANS;
> ...
> xfs_fs_freeze()
> ...
> xfs_quiesce_attr()
waits for all active
transactions
> ...
xfs_trans_alloc
-> blocks in xfs_wait_for_freeze
(thus doesn't get to _xfs_trans_alloc)
> _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...
I can't see the problem in this scheme. Note that we want
_xfs_trans_alloc to be able to create a transaction for
xfs_fs_log_dummy, so that we can write the dummy log record after
freezing out all other transactions, so that one is special cased
and doesn't do the xfs_wait_for_freeze.
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