Commit 21eed794 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

block: add new helper for disabling elevator switch when deleting disk 



Add new helper disable_elv_switch() and new flag QUEUE_FLAG_NO_ELV_SWITCH
for disabling elevator switch before deleting disk:

- originally flag QUEUE_FLAG_REGISTERED is added for preventing elevator
switch during removing disk, but this flag has been used widely for
other purposes, so add one new flag for disabling elevator switch only

- for avoiding deadlock risk, we have to move elevator queue
register/unregister out of elevator lock and queue freeze, which will be
done in next patch. However, this way adds small race window between elevator
switch and deleting ->queue_kobj, in which elevator queue register/unregister
could be run concurrently. The added helper will be used for avoiding the race
in the following patch.

- drain in-progress elevator switch before deleting disk

Suggested-by: default avatarNilay Shroff <nilay@linux.ibm.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarHannes Reinecke <hare@suse.de>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Reviewed-by: default avatarNilay Shroff <nilay@linux.ibm.com>
Link: https://lore.kernel.org/r/20250505141805.2751237-21-ming.lei@redhat.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 5c3d858c

block/blk-mq-debugfs.c

+1 −0
Original line number Diff line number Diff line
@@ -94,6 +94,7 @@ static const char *const blk_queue_flag_name[] = { 
	QUEUE_FLAG_NAME(HCTX_ACTIVE),

	QUEUE_FLAG_NAME(SQ_SCHED),

	QUEUE_FLAG_NAME(DISABLE_WBT_DEF),

	QUEUE_FLAG_NAME(NO_ELV_SWITCH),

};

#undef QUEUE_FLAG_NAME

block/elevator.c

+10 −3
Original line number Diff line number Diff line
@@ -680,6 +680,9 @@ void elevator_set_default(struct request_queue *q) 
	};

	int err = 0;



	/* now we allow to switch elevator */

	blk_queue_flag_clear(QUEUE_FLAG_NO_ELV_SWITCH, q);



	if (q->tag_set->flags & BLK_MQ_F_NO_SCHED_BY_DEFAULT)

		return;
@@ -744,9 +747,13 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf, 
	elv_iosched_load_module(ctx.name);



	down_read(&set->update_nr_hwq_lock);

	if (!blk_queue_no_elv_switch(q)) {

		ret = elevator_change(q, &ctx);

		if (!ret)

			ret = count;

	} else {

		ret = -ENOENT;

	}

	up_read(&set->update_nr_hwq_lock);

	return ret;

}

block/genhd.c

+13 −0
Original line number Diff line number Diff line
@@ -764,6 +764,16 @@ static void __del_gendisk(struct gendisk *disk) 
		blk_unfreeze_release_lock(q);

}



static void disable_elv_switch(struct request_queue *q)

{

	struct blk_mq_tag_set *set = q->tag_set;

	WARN_ON_ONCE(!queue_is_mq(q));



	down_write(&set->update_nr_hwq_lock);

	blk_queue_flag_set(QUEUE_FLAG_NO_ELV_SWITCH, q);

	up_write(&set->update_nr_hwq_lock);

}



/**

 * del_gendisk - remove the gendisk

 * @disk: the struct gendisk to remove
@@ -792,6 +802,9 @@ void del_gendisk(struct gendisk *disk) 
		__del_gendisk(disk);

	} else {

		set = disk->queue->tag_set;



		disable_elv_switch(disk->queue);



		memflags = memalloc_noio_save();

		down_read(&set->update_nr_hwq_lock);

		__del_gendisk(disk);

include/linux/blkdev.h

+3 −0
Original line number Diff line number Diff line
@@ -642,6 +642,7 @@ enum { 
	QUEUE_FLAG_HCTX_ACTIVE,		/* at least one blk-mq hctx is active */

	QUEUE_FLAG_SQ_SCHED,		/* single queue style io dispatch */

	QUEUE_FLAG_DISABLE_WBT_DEF,	/* for sched to disable/enable wbt */

	QUEUE_FLAG_NO_ELV_SWITCH,	/* can't switch elevator any more */

	QUEUE_FLAG_MAX

};
@@ -679,6 +680,8 @@ void blk_queue_flag_clear(unsigned int flag, struct request_queue *q); 
	((q)->limits.features & BLK_FEAT_SKIP_TAGSET_QUIESCE)

#define blk_queue_disable_wbt(q)	\

	test_bit(QUEUE_FLAG_DISABLE_WBT_DEF, &(q)->queue_flags)

#define blk_queue_no_elv_switch(q)	\

	test_bit(QUEUE_FLAG_NO_ELV_SWITCH, &(q)->queue_flags)



extern void blk_set_pm_only(struct request_queue *q);

extern void blk_clear_pm_only(struct request_queue *q);