[PATCH] blk: fix gendisk->in_flight accounting during barrier sequence

While executing barrrier sequence, the bar_rq which carries actual
write was accounted as normal IO on completion, while it wasn't on
queueing.  This caused gendisk->in_flight to be decremented by 1 after
each barrier thus messed up statistics.

This patch makes bar_rq not accounted as normal IO.  As the containing
barrier request as a whole is accounted, part of it shouldn't be.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index eac48bec147..7eb36c53f4b 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -3452,7 +3452,12 @@ void end_that_request_last(struct request *req, int uptodate)
         if (unlikely(laptop_mode) && blk_fs_request(req))
                 laptop_io_completion();
 
-        if (disk && blk_fs_request(req)) {
+        /*
+         * Account IO completion.  bar_rq isn't accounted as a normal
+         * IO on queueing nor completion.  Accounting the containing
+         * request is enough.
+         */
+        if (disk && blk_fs_request(req) && req != &req->q->bar_rq) {
                 unsigned long duration = jiffies - req->start_time;
                 const int rw = rq_data_dir(req);