[PATCH v3 4/5] blk-wbt: don't enable throttling if default elevator is bfq

[Yu Kuai <yukuai3@xxxxxxxxxx>]

Commit b5dc5d4d1f4f ("block,bfq: Disable writeback throttling") tries to
disable wbt for bfq, it's done by calling wbt_disable_default() in
bfq_init_queue(). However, wbt is still enabled if default elevator is
bfq:

device_add_disk
 elevator_init_mq
  bfq_init_queue
   wbt_disable_default -> done nothing

 blk_register_queue
  wbt_enable_default -> wbt is enabled

Fix the problem by adding a new flag ELEVATOR_FLAG_DISBALE_WBT, bfq
will set the flag in bfq_init_queue, and following wbt_enable_default()
won't enable wbt while the flag is set.

Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 block/bfq-iosched.c | 2 ++
 block/blk-wbt.c     | 8 +++++++-
 block/elevator.h    | 3 ++-
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index fec52968fe07..f67ed271baa9 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -7037,6 +7037,7 @@ static void bfq_exit_queue(struct elevator_queue *e)
 
 #ifdef CONFIG_BFQ_GROUP_IOSCHED
 	blkcg_deactivate_policy(bfqd->queue, &blkcg_policy_bfq);
+	clear_bit(ELEVATOR_FLAG_DISABLE_WBT, &e->flags);
 	wbt_enable_default(bfqd->queue);
 #else
 	spin_lock_irq(&bfqd->lock);
@@ -7191,6 +7192,7 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
 	blk_queue_flag_set(QUEUE_FLAG_SQ_SCHED, q);
 
 #ifdef CONFIG_BFQ_GROUP_IOSCHED
+	set_bit(ELEVATOR_FLAG_DISABLE_WBT, &eq->flags);
 	wbt_disable_default(q);
 #endif
 	blk_stat_enable_accounting(q);
diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index 68851c2c02d2..279f8dc1e952 100644
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -27,6 +27,7 @@
 
 #include "blk-wbt.h"
 #include "blk-rq-qos.h"
+#include "elevator.h"
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/wbt.h>
@@ -645,9 +646,14 @@ void wbt_set_write_cache(struct request_queue *q, bool write_cache_on)
  */
 void wbt_enable_default(struct request_queue *q)
 {
-	struct rq_qos *rqos = wbt_rq_qos(q);
+	struct rq_qos *rqos;
+
+	if (q->elevator &&
+	    test_bit(ELEVATOR_FLAG_DISABLE_WBT, &q->elevator->flags))
+		return;
 
 	/* Throttling already enabled? */
+	rqos = wbt_rq_qos(q);
 	if (rqos) {
 		if (RQWB(rqos)->enable_state == WBT_STATE_OFF_DEFAULT)
 			RQWB(rqos)->enable_state = WBT_STATE_ON_DEFAULT;
diff --git a/block/elevator.h b/block/elevator.h
index ed574bf3e629..75382471222d 100644
--- a/block/elevator.h
+++ b/block/elevator.h
@@ -104,7 +104,8 @@ struct elevator_queue
 	DECLARE_HASHTABLE(hash, ELV_HASH_BITS);
 };
 
-#define ELEVATOR_FLAG_REGISTERED 0
+#define ELEVATOR_FLAG_REGISTERED	0
+#define ELEVATOR_FLAG_DISABLE_WBT	1
 
 /*
  * block elevator interface
-- 
2.31.1