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

[Jianpeng Ma]

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 <majianp...@gmail.com>
Signed-off-by: Jens Axboe <ax...@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);
-- 
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