dm: do not use waitqueue for request-based DM

Given request-based DM now uses blk-mq's blk_mq_queue_inflight() to
determine if outstanding IO has completed (and DM has no control over
the blk-mq state machine used to track outstanding IO) it is unsafe to
wakeup waiter (dm_wait_for_completion) before blk-mq has cleared a
request's state bits (e.g. MQ_RQ_IN_FLIGHT or MQ_RQ_COMPLETE).  As
such dm_wait_for_completion() could be left to wait indefinitely if no
other requests complete.

Fix this by eliminating request-based DM's use of waitqueue to wait
for blk-mq requests to complete in dm_wait_for_completion.
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Depends-on: 3c94d83c ("blk-mq: change blk_mq_queue_busy() to blk_mq_queue_inflight()")
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-rq.c

@@ -146,10 +146,6 @@ static void rq_end_stats(struct mapped_device *md, struct request *orig)
  */
 static void rq_completed(struct mapped_device *md)
 {
-	/* nudge anyone waiting on suspend queue */
-	if (unlikely(wq_has_sleeper(&md->wait)))
-		wake_up(&md->wait);
-
 	/*
 	 * dm_put() must be at the end of this function. See the comment above
 	 */

drivers/md/dm.c

@@ -654,28 +654,6 @@ static void free_tio(struct dm_target_io *tio)
 	bio_put(&tio->clone);
 }
 
-static bool md_in_flight_bios(struct mapped_device *md)
-{
-	int cpu;
-	struct hd_struct *part = &dm_disk(md)->part0;
-	long sum = 0;
-
-	for_each_possible_cpu(cpu) {
-		sum += part_stat_local_read_cpu(part, in_flight[0], cpu);
-		sum += part_stat_local_read_cpu(part, in_flight[1], cpu);
-	}
-
-	return sum != 0;
-}
-
-static bool md_in_flight(struct mapped_device *md)
-{
-	if (queue_is_mq(md->queue))
-		return blk_mq_queue_inflight(md->queue);
-	else
-		return md_in_flight_bios(md);
-}
-
 u64 dm_start_time_ns_from_clone(struct bio *bio)
 {
 	struct dm_target_io *tio = container_of(bio, struct dm_target_io, clone);
@@ -2470,15 +2448,29 @@ void dm_put(struct mapped_device *md)
 }
 EXPORT_SYMBOL_GPL(dm_put);
 
-static int dm_wait_for_completion(struct mapped_device *md, long task_state)
+static bool md_in_flight_bios(struct mapped_device *md)
+{
+	int cpu;
+	struct hd_struct *part = &dm_disk(md)->part0;
+	long sum = 0;
+
+	for_each_possible_cpu(cpu) {
+		sum += part_stat_local_read_cpu(part, in_flight[0], cpu);
+		sum += part_stat_local_read_cpu(part, in_flight[1], cpu);
+	}
+
+	return sum != 0;
+}
+
+static int dm_wait_for_bios_completion(struct mapped_device *md, long task_state)
 {
 	int r = 0;
 	DEFINE_WAIT(wait);
 
-	while (1) {
+	while (true) {
 		prepare_to_wait(&md->wait, &wait, task_state);
 
-		if (!md_in_flight(md))
+		if (!md_in_flight_bios(md))
 			break;
 
 		if (signal_pending_state(task_state, current)) {
@@ -2493,6 +2485,28 @@ static int dm_wait_for_completion(struct mapped_device *md, long task_state)
 	return r;
 }
 
+static int dm_wait_for_completion(struct mapped_device *md, long task_state)
+{
+	int r = 0;
+
+	if (!queue_is_mq(md->queue))
+		return dm_wait_for_bios_completion(md, task_state);
+
+	while (true) {
+		if (!blk_mq_queue_inflight(md->queue))
+			break;
+
+		if (signal_pending_state(task_state, current)) {
+			r = -EINTR;
+			break;
+		}
+
+		msleep(5);
+	}
+
+	return r;
+}
+
 /*
  * Process the deferred bios
  */