Re: [dm-devel] [BUG] pvmove corrupting XFS filesystems (was Re: [BUG] Internal error xfs_dir2_data_reada_verify)

[Matteo Frigo <athena@xxxxxxxx>]

Dave Chinner <david@xxxxxxxxxxxxx> writes:

> On Wed, Feb 27, 2013 at 01:04:14AM +0000, Alasdair G Kergon wrote:
>> (Quick pointers that might be relevant)
>> 
>> EAGAIN, I'm not aware of dm itself returning that on the i/o path.
>
> Neither am I, but it's coming from somewhere in the IO path...

Well, I don't really know anything about this topic, so I may be
completely off the mark, but dm-raid1.c:mirror_map() does indeed return
EWOULDBLOCK, and EWOULDBLOCK is #define'd to be EAGAIN, so it seems to
me that dm-raid1 does indeed return EAGAIN for "rw == READA" (which I
assume is read-ahead) if the "region is not in-sync":

        /*
         * If region is not in-sync queue the bio.
         */
        if (!r || (r == -EWOULDBLOCK)) {
                if (rw == READA)
                        return -EWOULDBLOCK;

                queue_bio(ms, bio, rw);
                return DM_MAPIO_SUBMITTED;
        }

Regards,
MF