On Fri 09-03-12 10:20:41, Dave Chinner wrote:
> On Mon, Mar 05, 2012 at 05:01:09PM +0100, Jan Kara wrote:
> > Generic code now blocks all writers from standard write paths. So we block all
> > writers coming from ioctl and replace blocking of transactions on frozen
> > filesystem with a debugging check. As a bonus, we get a protection of ioctl
> > against racing remount read-only. We also convert xfs_file_aio_write() to a
> > non-racy freeze protection.
> ....
> > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> > index 329b06a..6468a2a 100644
> > --- a/fs/xfs/xfs_trans.c
> > +++ b/fs/xfs/xfs_trans.c
> > @@ -577,7 +577,6 @@ xfs_trans_alloc(
> > xfs_mount_t *mp,
> > uint type)
> > {
> > - xfs_wait_for_freeze(mp, SB_FREEZE_TRANS);
> > return _xfs_trans_alloc(mp, type, KM_SLEEP);
> > }
>
> So what is there to stop internal XFS threads from starting
> transactions when the filesystem is frozen? Previously this
> SB_FREEZE_TRANS would guarantee even internal fucntions would get
> stopped, but now there's nothing?
>
> I do beleive that ext4 has the same problem (the issue reported with
> the lazy inode init background thread), and I can see that any other
> filesystem that can make modifications via internal triggers will
> see the same problem - freeze doesn't block them any more...
Yes, I'll have to audit filesystem internal threads. I forgot about these
in the first round. Most of them shouldn't have anything to do because the
filesystem is clean but there are exceptions as ext4 lazyinit has shown.
Honza
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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