From 70283b25ae50d37458ad296e1ff39df55384a686 Mon Sep 17 00:00:00 2001
From: Bart Van Assche <bvanassche@acm.org>
Date: Wed, 28 Nov 2012 13:46:45 +0100
Subject: [PATCH] --- yaml --- r: 345670 b: refs/heads/master c:
 24faf6f604efe18236bded4303009fc252913bf0 h: refs/heads/master v: v3

---
 [refs]                       |  2 +-
 trunk/block/blk-core.c       | 10 ++++++++++
 trunk/include/linux/blkdev.h |  6 ++++++
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/[refs] b/[refs]
index 9838ebcd9ad9..d81a74549d25 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 704605711ef048a7c6ad2ec599f15d2e0baf86b2
+refs/heads/master: 24faf6f604efe18236bded4303009fc252913bf0
diff --git a/trunk/block/blk-core.c b/trunk/block/blk-core.c
index 9fb23537c7ad..473015ee28a2 100644
--- a/trunk/block/blk-core.c
+++ b/trunk/block/blk-core.c
@@ -309,7 +309,16 @@ inline void __blk_run_queue_uncond(struct request_queue *q)
 	if (unlikely(blk_queue_dead(q)))
 		return;
 
+	/*
+	 * Some request_fn implementations, e.g. scsi_request_fn(), unlock
+	 * the queue lock internally. As a result multiple threads may be
+	 * running such a request function concurrently. Keep track of the
+	 * number of active request_fn invocations such that blk_drain_queue()
+	 * can wait until all these request_fn calls have finished.
+	 */
+	q->request_fn_active++;
 	q->request_fn(q);
+	q->request_fn_active--;
 }
 
 /**
@@ -408,6 +417,7 @@ static void __blk_drain_queue(struct request_queue *q, bool drain_all)
 			__blk_run_queue(q);
 
 		drain |= q->nr_rqs_elvpriv;
+		drain |= q->request_fn_active;
 
 		/*
 		 * Unfortunately, requests are queued at and tracked from
diff --git a/trunk/include/linux/blkdev.h b/trunk/include/linux/blkdev.h
index 8bc46c250ca4..c9d233e727f2 100644
--- a/trunk/include/linux/blkdev.h
+++ b/trunk/include/linux/blkdev.h
@@ -378,6 +378,12 @@ struct request_queue {
 
 	unsigned int		nr_sorted;
 	unsigned int		in_flight[2];
+	/*
+	 * Number of active block driver functions for which blk_drain_queue()
+	 * must wait. Must be incremented around functions that unlock the
+	 * queue_lock internally, e.g. scsi_request_fn().
+	 */
+	unsigned int		request_fn_active;
 
 	unsigned int		rq_timeout;
 	struct timer_list	timeout;