md: fix data corruption when a degraded raid5 array is reshaped

We currently do not wait for the block from the missing device to be
computed from parity before copying data to the new stripe layout.

The change in the raid6 code is not techincally needed as we don't delay
data block recovery in the same way for raid6 yet.  But making the change
now is safer long-term.

This bug exists in 2.6.23 and 2.6.24-rc

Cc: <stable@kernel.org>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Acked-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/md/raid5.c

@@ -2865,7 +2865,8 @@ static void handle_stripe5(struct stripe_head *sh)
 		md_done_sync(conf->mddev, STRIPE_SECTORS, 1);
 	}
 
-	if (s.expanding && s.locked == 0)
+	if (s.expanding && s.locked == 0 &&
+	    !test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending))
 		handle_stripe_expansion(conf, sh, NULL);
 
 	if (sh->ops.count)
@@ -3067,7 +3068,8 @@ static void handle_stripe6(struct stripe_head *sh, struct page *tmp_page)
 		md_done_sync(conf->mddev, STRIPE_SECTORS, 1);
 	}
 
-	if (s.expanding && s.locked == 0)
+	if (s.expanding && s.locked == 0 &&
+	    !test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending))
 		handle_stripe_expansion(conf, sh, &r6s);
 
 	spin_unlock(&sh->lock);