[PATCH] block: fix blk_queue_end_tag()

[Dan Williams <dan.j.williams@intel.com>]

Commit 5e081591 "block: warn if tag is greater than real_max_depth"
cleaned up blk_queue_end_tag() to warn when the tag is truly invalid
(greater than real_max_depth).  However, it changed behavior in the tag
< max_depth case to not end the request.  Leading to triggering of
BUG_ON(blk_queued_rq(rq)) in the request completion path:

  http://marc.info/?l=linux-kernel&m=132204370518629&w=2

In order to allow blk_queue_resize_tags() to shrink the tag space
blk_queue_end_tag() must always complete tags with a value less than
real_max_depth regardless of the current max_depth.

Cc: Tao Ma <boyu.mt@taobao.com>
Reported-by: Meelis Roos <mroos@ut.ee>
Reported-by: Ed Nadolski <edmund.nadolski@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
Functionally the same as Tao Ma's fix [1], but just moves the warn into the
if() directly.

[1]: http://marc.info/?l=linux-scsi&m=132439698602441&w=2

--
Dan

 block/blk-tag.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/blk-tag.c b/block/blk-tag.c
index e74d6d1..6e61262 100644
--- a/block/blk-tag.c
+++ b/block/blk-tag.c
@@ -286,12 +286,13 @@ void blk_queue_end_tag(struct request_queue *q, struct request *rq)
 
 	BUG_ON(tag == -1);
 
-	if (unlikely(tag >= bqt->max_depth)) {
+	if (WARN_ONCE(tag >= bqt->real_max_depth,
+		      "%s: tag %d greater than tag map size: %d\n",
+		      __func__, tag, bqt->real_max_depth)) {
 		/*
 		 * This can happen after tag depth has been reduced.
 		 * But tag shouldn't be larger than real_max_depth.
 		 */
-		WARN_ON(tag >= bqt->real_max_depth);
 		return;
 	}