From eab6fcf772e91a16428e0f3262e6b4ef81705f79 Mon Sep 17 00:00:00 2001
From: sunguoshuai <sunguoshuai@huawei.com>
Date: Tue, 22 Jan 2019 21:29:56 -0500
Subject: [PATCH] multipathd: disable queueing for recreated map in
 uev_remove_map

reason:disable queueing for recreated map in uev_remove_map
---
 multipathd/main.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/multipathd/main.c b/multipathd/main.c
index 8baf9ab..23fb9d4 100644
--- a/multipathd/main.c
+++ b/multipathd/main.c
@@ -674,7 +674,7 @@ uev_add_map (struct uevent * uev, struct vectors * vecs)
 	char *alias;
 	int major = -1, minor = -1, rc;
 
-	condlog(3, "%s: add map (uevent)", uev->kernel);
+	condlog(2, "%s: add map (uevent)", uev->kernel);
 	alias = uevent_get_dm_name(uev);
 	if (!alias) {
 		condlog(3, "%s: No DM_NAME in uevent", uev->kernel);
@@ -793,7 +793,26 @@ uev_remove_map (struct uevent * uev, struct vectors * vecs)
 			uev->kernel, mpp->alias, alias);
 		goto out;
 	}
-
+		/*
+		 * There may be a race window here:
+		 * 1. all paths gone, causing map flushed both from multipathd and kernel
+		 * 2. paths regenerated, causing multipathd creating the map again.
+		 * 1 will generate a remove uevent which can be handled after 2,
+		 * so we can disable queueing for the map created by 2 here temporarily
+		 * and let the change uevent (generated by 2) calling uev_add_map
+		 * ->setup_multipath to set queueing again. This can prevent
+		 * the deadlock in this race window.
+		 *
+		 * The possible deadlock is: all udevd workers hangs in
+		 * devices because of queue_if_no_path, so no udevd workers
+		 * can handle new event and since multipathd will remove the map,
+		 * the checkerloop cannot check this map's retry tick timeout
+		 * and cancel the io hang which makes the udevd worker hang forever.
+		 * multipathd cannot receive any uevent from udevd because all
+		 * udevd workers hang there so the map cannot be recreated
+		 * again which makes a deadlock.
+		 */
+		dm_queue_if_no_path(alias, 0);
 	remove_map_and_stop_waiter(mpp, vecs);
 out:
 	lock_cleanup_pop(vecs->lock);
-- 
1.8.3.1