md/raid6: Fix raid-6 read-error correction in degraded state

Fix: Raid-6 was not trying to correct a read-error when in
singly-degraded state and was instead dropping one more device, going to
doubly-degraded state. This patch fixes this behaviour.
Tested-by: NJanos Haar <janos.haar@netcenter.hu>
Signed-off-by: NGabriele A. Trombetti <g.trombetti.lkrnl1213@logicschema.com>
Reported-by: NJanos Haar <janos.haar@netcenter.hu>
Signed-off-by: NNeilBrown <neilb@suse.de>
Cc: stable@kernel.org

drivers/md/raid5.c

@@ -1527,7 +1527,7 @@ static void raid5_end_read_request(struct bio * bi, int error)
 
 		clear_bit(R5_UPTODATE, &sh->dev[i].flags);
 		atomic_inc(&rdev->read_errors);
-		if (conf->mddev->degraded)
+		if (conf->mddev->degraded >= conf->max_degraded)
 			printk_rl(KERN_WARNING
 				  "raid5:%s: read error not correctable "
 				  "(sector %llu on %s).\n",