block: reorganize queue draining

Reorganize queue draining related code in preparation of queue exit
changes.

* Factor out actual draining from elv_quiesce_start() to
  blk_drain_queue().

* Make elv_quiesce_start/end() responsible for their own locking.

* Replace open-coded ELVSWITCH clearing in elevator_switch() with
  elv_quiesce_end().

This patch doesn't cause any visible functional difference.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-core.c b/block/blk-core.c
index a3d2fdc..149149d 100644 (file)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -28,6 +28,7 @@
 #include <linux/task_io_accounting_ops.h>
 #include <linux/fault-inject.h>
 #include <linux/list_sort.h>
+#include <linux/delay.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/block.h>
@@ -345,6 +346,33 @@ void blk_put_queue(struct request_queue *q)
 }
 EXPORT_SYMBOL(blk_put_queue);
 
+/**
+ * blk_drain_queue - drain requests from request_queue
+ * @q: queue to drain
+ *
+ * Drain ELV_PRIV requests from @q.  The caller is responsible for ensuring
+ * that no new requests which need to be drained are queued.
+ */
+void blk_drain_queue(struct request_queue *q)
+{
+       while (true) {
+               int nr_rqs;
+
+               spin_lock_irq(q->queue_lock);
+
+               elv_drain_elevator(q);
+
+               __blk_run_queue(q);
+               nr_rqs = q->rq.elvpriv;
+
+               spin_unlock_irq(q->queue_lock);
+
+               if (!nr_rqs)
+                       break;
+               msleep(10);
+       }
+}
+
 /*
  * Note: If a driver supplied the queue lock, it is disconnected
  * by this function. The actual state of the lock doesn't matter

diff --git a/block/blk.h b/block/blk.h
index da247ba..2b66dc2 100644 (file)
--- a/block/blk.h
+++ b/block/blk.h
@@ -15,6 +15,7 @@ void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
                        struct bio *bio);
 int blk_rq_append_bio(struct request_queue *q, struct request *rq,
                      struct bio *bio);
+void blk_drain_queue(struct request_queue *q);
 void blk_dequeue_request(struct request *rq);
 void __blk_queue_free_tags(struct request_queue *q);
 bool __blk_end_bidi_request(struct request *rq, int error,

diff --git a/block/elevator.c b/block/elevator.c
index cb332cb..74a277f 100644 (file)
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -31,7 +31,6 @@
 #include <linux/slab.h>
 #include <linux/init.h>
 #include <linux/compiler.h>
-#include <linux/delay.h>
 #include <linux/blktrace_api.h>
 #include <linux/hash.h>
 #include <linux/uaccess.h>
@@ -606,43 +605,35 @@ void elv_requeue_request(struct request_queue *q, struct request *rq)
 void elv_drain_elevator(struct request_queue *q)
 {
        static int printed;
+
+       lockdep_assert_held(q->queue_lock);
+
        while (q->elevator->ops->elevator_dispatch_fn(q, 1))
                ;
-       if (q->nr_sorted == 0)
-               return;
-       if (printed++ < 10) {
+       if (q->nr_sorted && printed++ < 10) {
                printk(KERN_ERR "%s: forced dispatching is broken "
                       "(nr_sorted=%u), please report this\n",
                       q->elevator->elevator_type->elevator_name, q->nr_sorted);
        }
 }
 
-/*
- * Call with queue lock held, interrupts disabled
- */
 void elv_quiesce_start(struct request_queue *q)
 {
        if (!q->elevator)
                return;
 
+       spin_lock_irq(q->queue_lock);
        queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
+       spin_unlock_irq(q->queue_lock);
 
-       /*
-        * make sure we don't have any requests in flight
-        */
-       elv_drain_elevator(q);
-       while (q->rq.elvpriv) {
-               __blk_run_queue(q);
-               spin_unlock_irq(q->queue_lock);
-               msleep(10);
-               spin_lock_irq(q->queue_lock);
-               elv_drain_elevator(q);
-       }
+       blk_drain_queue(q);
 }
 
 void elv_quiesce_end(struct request_queue *q)
 {
+       spin_lock_irq(q->queue_lock);
        queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
+       spin_unlock_irq(q->queue_lock);
 }
 
 void __elv_add_request(struct request_queue *q, struct request *rq, int where)
@@ -972,7 +963,6 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
        /*
         * Turn on BYPASS and drain all requests w/ elevator private data
         */
-       spin_lock_irq(q->queue_lock);
        elv_quiesce_start(q);
 
        /*
@@ -983,8 +973,8 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
        /*
         * attach and start new elevator
         */
+       spin_lock_irq(q->queue_lock);
        elevator_attach(q, e, data);
-
        spin_unlock_irq(q->queue_lock);
 
        if (old_elevator->registered) {
@@ -999,9 +989,7 @@ 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);
-       spin_lock_irq(q->queue_lock);
        elv_quiesce_end(q);
-       spin_unlock_irq(q->queue_lock);
 
        blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);
 
@@ -1015,10 +1003,7 @@ fail_register:
        elevator_exit(e);
        q->elevator = old_elevator;
        elv_register_queue(q);
-
-       spin_lock_irq(q->queue_lock);
-       queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
-       spin_unlock_irq(q->queue_lock);
+       elv_quiesce_end(q);
 
        return err;
 }