1 files changed, 25 insertions, 12 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index f2db628aa509..3b02ba351f8c 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -421,14 +421,18 @@ void blk_drain_queue(struct request_queue *q, bool drain_all)
  */
 void blk_queue_bypass_start(struct request_queue *q)
 {
+        bool drain;
+
         spin_lock_irq(q->queue_lock);
-        q->bypass_depth++;
+        drain = !q->bypass_depth++;
         queue_flag_set(QUEUE_FLAG_BYPASS, q);
         spin_unlock_irq(q->queue_lock);
 
-        blk_drain_queue(q, false);
-        /* ensure blk_queue_bypass() is %true inside RCU read lock */
-        synchronize_rcu();
+        if (drain) {
+                blk_drain_queue(q, false);
+                /* ensure blk_queue_bypass() is %true inside RCU read lock */
+                synchronize_rcu();
+        }
 }
 EXPORT_SYMBOL_GPL(blk_queue_bypass_start);
 
@@ -577,6 +581,15 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
          */
         q->queue_lock = &q->__queue_lock;
 
+        /*
+         * A queue starts its life with bypass turned on to avoid
+         * unnecessary bypass on/off overhead and nasty surprises during
+         * init.  The initial bypass will be finished at the end of
+         * blk_init_allocated_queue().
+         */
+        q->bypass_depth = 1;
+        __set_bit(QUEUE_FLAG_BYPASS, &q->queue_flags);
+
         if (blkcg_init_queue(q))
                 goto fail_id;
 
@@ -672,15 +685,15 @@ blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
 
         q->sg_reserved_size = INT_MAX;
 
-        /*
-         * all done
-         */
-        if (!elevator_init(q, NULL)) {
-                blk_queue_congestion_threshold(q);
-                return q;
-        }
+        /* init elevator */
+        if (elevator_init(q, NULL))
+                return NULL;
 
-        return NULL;
+        blk_queue_congestion_threshold(q);
+
+        /* all done, end the initial bypass */
+        blk_queue_bypass_end(q);
+        return q;
 }
 EXPORT_SYMBOL(blk_init_allocated_queue);