From c51bc66e4db9157937bea2101ae694eeb28522f2 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Thu, 21 Sep 2006 20:37:22 +0200
Subject: [PATCH] --- yaml --- r: 37592 b: refs/heads/master c:
 059af497c23492cb1ddcbba11c09dad385960bc0 h: refs/heads/master v: v3

---
 [refs]                  |  2 +-
 trunk/block/ll_rw_blk.c | 13 +++++++++----
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/[refs] b/[refs]
index 7d8efe135151..5e840f6a97aa 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 0fe23479577124bd2687e6783e39fa0fa4c28005
+refs/heads/master: 059af497c23492cb1ddcbba11c09dad385960bc0
diff --git a/trunk/block/ll_rw_blk.c b/trunk/block/ll_rw_blk.c
index f757ed413214..83425fb3c8db 100644
--- a/trunk/block/ll_rw_blk.c
+++ b/trunk/block/ll_rw_blk.c
@@ -1171,11 +1171,16 @@ int blk_queue_start_tag(request_queue_t *q, struct request *rq)
 		BUG();
 	}
 
-	tag = find_first_zero_bit(bqt->tag_map, bqt->max_depth);
-	if (tag >= bqt->max_depth)
-		return 1;
+	/*
+	 * Protect against shared tag maps, as we may not have exclusive
+	 * access to the tag map.
+	 */
+	do {
+		tag = find_first_zero_bit(bqt->tag_map, bqt->max_depth);
+		if (tag >= bqt->max_depth)
+			return 1;
 
-	__set_bit(tag, bqt->tag_map);
+	} while (test_and_set_bit(tag, bqt->tag_map));
 
 	rq->cmd_flags |= REQ_QUEUED;
 	rq->tag = tag;