md/raid5: abort any pending parity operations when array fails.

When the number of failed devices exceeds the allowed number
we must abort any active parity operations (checks or updates) as they
are no longer meaningful, and can lead to a BUG_ON in
handle_parity_checks6.

This bug was introduce by commit 6c0069c0
in 2.6.29.
Reported-by: Manish Katiyar <mkatiyar@gmail.com>
Tested-by: Manish Katiyar <mkatiyar@gmail.com>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Cc: stable@kernel.org

drivers/md/raid5.c

@@ -3159,10 +3159,14 @@ static void handle_stripe(struct stripe_head *sh)
 	/* check if the array has lost more than max_degraded devices and,
 	 * if so, some requests might need to be failed.
 	 */
-	if (s.failed > conf->max_degraded && s.to_read+s.to_write+s.written)
+	if (s.failed > conf->max_degraded) {
+		sh->check_state = 0;
+		sh->reconstruct_state = 0;
+		if (s.to_read+s.to_write+s.written)
 			handle_failed_stripe(conf, sh, &s, disks, &s.return_bi);
-	if (s.failed > conf->max_degraded && s.syncing)
+		if (s.syncing)
 			handle_failed_sync(conf, sh, &s);
+	}
 
 	/*
 	 * might be able to return some write requests if the parity blocks