From 4098378d2e976c9b371ae6bf83e802fb32187f50 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 cc493c1..9dd74ad 100644
--- a/multipathd/main.c
+++ b/multipathd/main.c
@@ -647,7 +647,7 @@ 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);
@@ -766,7 +766,26 @@ uev_remove_map (struct uevent * uev, struct vectors * vecs)
 			mpp->alias, mpp->dmi->minor, minor);
 		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);
 	orphan_paths(vecs->pathvec, mpp);
 	remove_map_and_stop_waiter(mpp, vecs);
 out:
-- 
1.8.3.1