Patch "blk-wbt: don't enable throttling if default elevator is bfq" has been added to the 6.1-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    blk-wbt: don't enable throttling if default elevator is bfq

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     blk-wbt-don-t-enable-throttling-if-default-elevator-.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 51938e4e6ade6005901b700cfe6ecdd7481af216
Author: Yu Kuai <yukuai3@xxxxxxxxxx>
Date:   Wed Oct 19 20:15:18 2022 +0800

    blk-wbt: don't enable throttling if default elevator is bfq
    
    [ Upstream commit 671fae5e51297fc76b3758ca2edd514858734a6a ]
    
    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>
    Reviewed-by: Christoph Hellwig <hch@xxxxxx>
    Link: https://lore.kernel.org/r/20221019121518.3865235-7-yukuai1@xxxxxxxxxxxxxxx
    Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
    Stable-dep-of: f814bdda774c ("blk-wbt: Fix detection of dirty-throttled tasks")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 52eb79d60a3f3..e4699291aee23 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -7059,6 +7059,7 @@ static void bfq_exit_queue(struct elevator_queue *e)
 #endif
 
 	blk_stat_disable_accounting(bfqd->queue);
+	clear_bit(ELEVATOR_FLAG_DISABLE_WBT, &e->flags);
 	wbt_enable_default(bfqd->queue);
 
 	kfree(bfqd);
@@ -7204,6 +7205,7 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
 	/* We dispatch from request queue wide instead of hw queue */
 	blk_queue_flag_set(QUEUE_FLAG_SQ_SCHED, q);
 
+	set_bit(ELEVATOR_FLAG_DISABLE_WBT, &eq->flags);
 	wbt_disable_default(q);
 	blk_stat_enable_accounting(q);
 
diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index c5a8c10028a08..afb1782b4255e 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>
@@ -638,11 +639,15 @@ 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;
+	bool disable_flag = q->elevator &&
+		    test_bit(ELEVATOR_FLAG_DISABLE_WBT, &q->elevator->flags);
 
 	/* Throttling already enabled? */
+	rqos = wbt_rq_qos(q);
 	if (rqos) {
-		if (RQWB(rqos)->enable_state == WBT_STATE_OFF_DEFAULT)
+		if (!disable_flag &&
+		    RQWB(rqos)->enable_state == WBT_STATE_OFF_DEFAULT)
 			RQWB(rqos)->enable_state = WBT_STATE_ON_DEFAULT;
 		return;
 	}
@@ -651,7 +656,7 @@ void wbt_enable_default(struct request_queue *q)
 	if (!blk_queue_registered(q))
 		return;
 
-	if (queue_is_mq(q))
+	if (queue_is_mq(q) && !disable_flag)
 		wbt_init(q);
 }
 EXPORT_SYMBOL_GPL(wbt_enable_default);
diff --git a/block/elevator.h b/block/elevator.h
index ed574bf3e629e..75382471222d1 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