block: stack unplug

MD raid1 prepares to dispatch request in unplug callback. If make_request in
low level queue also uses unplug callback to dispatch request, the low level
queue's unplug callback will not be called. Recheck the callback list helps
this case.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 7 insertions, 8 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 177ddcf356e6..35bf4fe8234c 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2913,17 +2913,16 @@ static void flush_plug_callbacks(struct blk_plug *plug)
 {
         LIST_HEAD(callbacks);
 
-        if (list_empty(&plug->cb_list))
-                return;
-
-        list_splice_init(&plug->cb_list, &callbacks);
+        while (!list_empty(&plug->cb_list)) {
+                list_splice_init(&plug->cb_list, &callbacks);
 
-        while (!list_empty(&callbacks)) {
-                struct blk_plug_cb *cb = list_first_entry(&callbacks,
+                while (!list_empty(&callbacks)) {
+                        struct blk_plug_cb *cb = list_first_entry(&callbacks,
                                                           struct blk_plug_cb,
                                                           list);
-                list_del(&cb->list);
-                cb->callback(cb);
+                        list_del(&cb->list);
+                        cb->callback(cb);
+                }
         }
 }