[dm-devel] [PATCH] dm-mpath: always return reservation conflict

[Christoph Hellwig]

From: Hannes Reinecke <hare at suse.de>

If dm-mpath encounters an reservation conflict it should not fail the
path (as communication with the target is not affected) but should
rather retry on another path. However, in doing so we might be inducing
a ping-pong between paths, with no guarantee of any forward progress.

And arguably a reservation conflict is an unexpected error, so we should
be passing it upwards to allow the application to take appropriate steps.

Signed-off-by: Hannes Reinecke <hare at suse.de>
Acked-by: Christoph Hellwig <hch at lst.de>
Tested-by: Christoph Hellwig <hch at lst.de>
---
 drivers/md/dm-mpath.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 7eac080..8d2f916 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -1555,16 +1555,22 @@ static int do_end_io(struct multipath *m, struct request *clone,
 	if (noretry_error(error))
 		return error;
 
-	if (mpio->pgpath)
+	/*
+	 * EBADE signals an reservation conflict.
+	 * We shouldn't fail the path here as we can communicate with
+	 * the target. We should failover to the next path, but in
+	 * doing so we might be causing a ping-pong between paths.
+	 * So just return the reservation conflict error.
+	 */
+	if (error == -EBADE)
+		r = error;
+	else if (mpio->pgpath)
 		fail_path(mpio->pgpath);
 
 	if (!atomic_read(&m->nr_valid_paths)) {
 		if (!test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) {
 			if (!must_push_back_rq(m))
 				r = -EIO;
-		} else {
-			if (error == -EBADE)
-				r = error;
 		}
 	}
 
-- 
2.1.4