block: blk-throttle should be drained regardless of q->elevator

Currently, blk_cleanup_queue() doesn't call elv_drain_elevator() if
q->elevator doesn't exist; however, bio based drivers don't have
elevator initialized but can still use blk-throttle.  This patch moves
q->elevator test inside blk_drain_queue() such that only
elv_drain_elevator() is skipped if !q->elevator.

-v2: loop can have registered queue which has NULL request_fn.  Make
     sure we don't call into __blk_run_queue() in such cases.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Vivek Goyal <vgoyal@redhat.com>
Fold in bug fix from Vivek.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-core.c b/block/blk-core.c
index 3a78b00edd71cfb7b667d50c9d3fe3265a5dba28..fccb2502112175112adc7db13cdadafe62cfa8c6 100644 (file)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -365,17 +365,24 @@ void blk_drain_queue(struct request_queue *q, bool drain_all)
 
                spin_lock_irq(q->queue_lock);
 
-               elv_drain_elevator(q);
+               /*
+                * The caller might be trying to drain @q before its
+                * elevator is initialized.
+                */
+               if (q->elevator)
+                       elv_drain_elevator(q);
+
                if (drain_all)
                        blk_throtl_drain(q);
 
                /*
                 * This function might be called on a queue which failed
-                * driver init after queue creation.  Some drivers
-                * (e.g. fd) get unhappy in such cases.  Kick queue iff
-                * dispatch queue has something on it.
+                * driver init after queue creation or is not yet fully
+                * active yet.  Some drivers (e.g. fd and loop) get unhappy
+                * in such cases.  Kick queue iff dispatch queue has
+                * something on it and @q has request_fn set.
                 */
-               if (!list_empty(&q->queue_head))
+               if (!list_empty(&q->queue_head) && q->request_fn)
                        __blk_run_queue(q);
 
                drain |= q->rq.elvpriv;
@@ -428,13 +435,8 @@ void blk_cleanup_queue(struct request_queue *q)
        spin_unlock_irq(lock);
        mutex_unlock(&q->sysfs_lock);
 
-       /*
-        * Drain all requests queued before DEAD marking.  The caller might
-        * be trying to tear down @q before its elevator is initialized, in
-        * which case we don't want to call into draining.
-        */
-       if (q->elevator)
-               blk_drain_queue(q, true);
+       /* drain all requests queued before DEAD marking */
+       blk_drain_queue(q, true);
 
        /* @q won't process any more request, flush async actions */
        del_timer_sync(&q->backing_dev_info.laptop_mode_wb_timer);
@@ -504,6 +506,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
        setup_timer(&q->backing_dev_info.laptop_mode_wb_timer,
                    laptop_mode_timer_fn, (unsigned long) q);
        setup_timer(&q->timeout, blk_rq_timed_out_timer, (unsigned long) q);
+       INIT_LIST_HEAD(&q->queue_head);
        INIT_LIST_HEAD(&q->timeout_list);
        INIT_LIST_HEAD(&q->icq_list);
        INIT_LIST_HEAD(&q->flush_queue[0]);