[PATCH] xfs: Fix re-use of EWOULDBLOCK during read on dm-mirror

[Dave Chinner]

On Fri, Dec 07, 2012 at 08:53:26PM +1100, Dave Chinner wrote:
> On Thu, Dec 06, 2012 at 05:39:17PM -0500, Jeff Mahoney wrote:
> > When using lvconvert to convert a linear mapping to a dm-raid1 mirror,
> > we encountered issues where the log would be flooded with messages like:
> > 
> > metadata I/O error: block 0xee7060 ("xfs_trans_read_buf") error 11 numblks 8
> > 
> > The cause is that dm-mirror (and striping, and others) will return
> > -EWOULDBLOCK for readahead requests while the mirror is rebuilding.
> 
> That's nasty - since when has DM been doing this? I doubt anything
> handles a EAGAIN error from the storage layer properly - it's not
> an error the filesystem expects from the lower layers at all.

Wow, it's been doing this since at least 2008 - it's taken the
best part of 5 years for someone to trip over this.....

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com