blk: clean up plug

Current code looks like inner plug gets flushed with a
blk_finish_plug(). Actually it's a nop. All requests/callbacks are added
to current->plug, while only outmost plug is assigned to current->plug.
So inner plug always has empty request/callback list, which makes
blk_flush_plug_list() a nop. This tries to make the code more clear.

Signed-off-by: Shaohua Li <shli@fb.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/block/blk-core.c b/block/blk-core.c
index 2e5020f37d55af2f944a1fbaa93dd19b161492b7..9dcfb8ec554b196f455762bd3abb7bf8f4ddbf26 100644 (file)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -3032,21 +3032,20 @@ void blk_start_plug(struct blk_plug *plug)
 {
        struct task_struct *tsk = current;
 
+       /*
+        * If this is a nested plug, don't actually assign it.
+        */
+       if (tsk->plug)
+               return;
+
        INIT_LIST_HEAD(&plug->list);
        INIT_LIST_HEAD(&plug->mq_list);
        INIT_LIST_HEAD(&plug->cb_list);
-
        /*
-        * If this is a nested plug, don't actually assign it. It will be
-        * flushed on its own.
+        * Store ordering should not be needed here, since a potential
+        * preempt will imply a full memory barrier
         */
-       if (!tsk->plug) {
-               /*
-                * Store ordering should not be needed here, since a potential
-                * preempt will imply a full memory barrier
-                */
-               tsk->plug = plug;
-       }
+       tsk->plug = plug;
 }
 EXPORT_SYMBOL(blk_start_plug);
 
@@ -3193,10 +3192,11 @@ void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 
 void blk_finish_plug(struct blk_plug *plug)
 {
+       if (plug != current->plug)
+               return;
        blk_flush_plug_list(plug, false);
 
-       if (plug == current->plug)
-               current->plug = NULL;
+       current->plug = NULL;
 }
 EXPORT_SYMBOL(blk_finish_plug);