block: make queue flags non-atomic

We can save some atomic ops in the IO path, if we clearly define
the rules of how to modify the queue flags.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 10 insertions, 3 deletions

diff --git a/block/elevator.c b/block/elevator.c
index 88318c383608..e8a90fe23424 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -1070,7 +1070,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
          */
         spin_lock_irq(q->queue_lock);
 
-        set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
+        queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
 
         elv_drain_elevator(q);
 
@@ -1104,7 +1104,10 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
          * finally exit old elevator and turn off BYPASS.
          */
         elevator_exit(old_elevator);
-        clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
+        spin_lock_irq(q->queue_lock);
+        queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
+        spin_unlock_irq(q->queue_lock);
+
         return 1;
 
 fail_register:
@@ -1115,7 +1118,11 @@ fail_register:
         elevator_exit(e);
         q->elevator = old_elevator;
         elv_register_queue(q);
-        clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
+
+        spin_lock_irq(q->queue_lock);
+        queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
+        spin_unlock_irq(q->queue_lock);
+
         return 0;
 }