block: trace all devices plug operation

In func blk_queue_bio, if list of plug is empty,it will call
blk_trace_plug.
If process deal with a single device,it't ok.But if process deal with
multi devices,it only trace the first device.
Using request_count to judge, it can soleve this problem.

In addition, i modify the comment.

Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 2 insertions, 4 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 93a18d1d3da8..91037f74668e 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1549,11 +1549,9 @@ get_rq:
         if (plug) {
                 /*
                  * If this is the first request added after a plug, fire
-                 * of a plug trace. If others have been added before, check
-                 * if we have multiple devices in this plug. If so, make a
-                 * note to sort the list before dispatch.
+                 * of a plug trace.
                  */
-                if (list_empty(&plug->list))
+                if (!request_count)
                         trace_block_plug(q);
                 else {
                         if (request_count >= BLK_MAX_REQUEST_COUNT) {