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Re: [dm-devel] [BUG] pvmove corrupting XFS filesystems (was Re: [BUG] In

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [dm-devel] [BUG] pvmove corrupting XFS filesystems (was Re: [BUG] Internal error xfs_dir2_data_reada_verify)
From: Matteo Frigo <athena@xxxxxxxx>
Date: Tue, 26 Feb 2013 21:21:44 -0500
Cc: dm-devel@xxxxxxxxxx, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130227014900.GY5551@dastard> (Dave Chinner's message of "Wed, 27 Feb 2013 12:49:00 +1100")
References: <87d2vnc34r.fsf@xxxxxxxx> <20130226044039.GM5551@dastard> <20130227010414.GD1514@xxxxxxxxxxxxxxxxxx> <20130227014900.GY5551@dastard>
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.1 (gnu/linux)
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;


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