block: fix inconsistency in I/O stat accounting code

This forces in_flight to be zero when turning off or on the I/O stat
accounting and stops updating I/O stats in attempt_merge() when
accounting is turned off.

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 17 insertions, 12 deletions

diff --git a/block/blk-merge.c b/block/blk-merge.c
index e39cb24b7679..63760ca3da0f 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -338,6 +338,22 @@ static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
         return 1;
 }
 
+static void blk_account_io_merge(struct request *req)
+{
+        if (blk_do_io_stat(req)) {
+                struct hd_struct *part;
+                int cpu;
+
+                cpu = part_stat_lock();
+                part = disk_map_sector_rcu(req->rq_disk, req->sector);
+
+                part_round_stats(cpu, part);
+                part_dec_in_flight(part);
+
+                part_stat_unlock();
+        }
+}
+
 /*
  * Has to be called with the request spinlock acquired
  */
@@ -386,18 +402,7 @@ static int attempt_merge(struct request_queue *q, struct request *req,
 
         elv_merge_requests(q, req, next);
 
-        if (req->rq_disk) {
-                struct hd_struct *part;
-                int cpu;
-
-                cpu = part_stat_lock();
-                part = disk_map_sector_rcu(req->rq_disk, req->sector);
-
-                part_round_stats(cpu, part);
-                part_dec_in_flight(part);
-
-                part_stat_unlock();
-        }
+        blk_account_io_merge(req);
 
         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
         if (blk_rq_cpu_valid(next))