[PATCH 2/3 V1] block: Fix not tracing all device plug-operation.

["Jianpeng Ma" <majianpeng@gmail.com>]

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If process handled two or more devices,there will not be trace some
devices plug-operation.

V0-->V1
Fix a bug when insert a req to plug-list which already had the same request-queue, it should
used list_add not list_add_tail.

Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 block/blk-core.c |   16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 7a3abc6..034f186 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1521,11 +1521,25 @@ get_rq:
 				struct request *__rq;
 
 				__rq = list_entry_rq(plug->list.prev);
-				if (__rq->q != q)
+				if (__rq->q != q) {
 					plug->should_sort = 1;
+					trace_block_plug(q);
+				}
+			} else {
+				struct request *__rq;
+				list_for_each_entry_reverse(__rq, &plug->list,
+					queuelist) {
+					if (__rq->q == q) {
+						list_add(&req->queuelist,
+							&__rq->queuelist);
+						goto stat_acct;
+					}
+				}
+				trace_block_plug(q);
 			}
 		}
 		list_add_tail(&req->queuelist, &plug->list);
+stat_acct:
 		drive_stat_acct(req, 1);
 	} else {
 		spin_lock_irq(q->queue_lock);
-- 
1.7.9.5
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