[V2,3/3] block: use blk_mq_no_io() for avoiding lock dependency

Commit Message

Ming Lei April 3, 2025, 2:52 a.m. UTC

Lock implied in blk_mq_enter_no_io() won't connect with any lock in IO
code paths now, so use it to prevent IO from entering queue for avoiding
lock dependency between freeze lock and elevator lock, and we have got
many such reports.

Reported-by: [e-mail]
Closes: https://lore.kernel.org/linux-block/[e-mail]
Reported-by: Valdis Klētnieks <[e-mail]>
Closes: https://lore.kernel.org/linux-block/7755.1743228130@turing-police/#t
Reviewed-by: Nilay Shroff <[e-mail]>
Signed-off-by: Ming Lei <[e-mail]>
---
 block/blk-mq.c    | 7 ++-----
 block/blk-sysfs.c | 8 ++++----
 block/elevator.c  | 4 ++--
 3 files changed, 8 insertions(+), 11 deletions(-)

Comments

Christoph Hellwig April 3, 2025, 5:44 a.m. UTC | #1

On Thu, Apr 03, 2025 at 10:52:10AM +0800, Ming Lei wrote:
> Lock implied in blk_mq_enter_no_io() won't connect with any lock in IO
> code paths now, so use it to prevent IO from entering queue for avoiding
> lock dependency between freeze lock and elevator lock, and we have got
> many such reports.

Please explain what this actually fixes here.

Patch

diff --git a/block/blk-mq.c b/block/blk-mq.c
index d117fa18b394..65b6671d41f3 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -4891,9 +4891,6 @@  int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
 	int ret;
 	unsigned long i;
 
-	if (WARN_ON_ONCE(!q->mq_freeze_depth))
-		return -EINVAL;
-
 	if (!set)
 		return -EINVAL;
 
@@ -5034,7 +5031,7 @@  static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
 
 	memflags = memalloc_noio_save();
 	list_for_each_entry(q, &set->tag_list, tag_set_list)
-		blk_mq_freeze_queue_nomemsave(q);
+		blk_mq_enter_no_io(q);
 
 	/*
 	 * Switch IO scheduler to 'none', cleaning up the data associated
@@ -5083,7 +5080,7 @@  static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
 		blk_mq_elv_switch_back(&head, q);
 
 	list_for_each_entry(q, &set->tag_list, tag_set_list)
-		blk_mq_unfreeze_queue_nomemrestore(q);
+		blk_mq_exit_no_io(q);
 	memalloc_noio_restore(memflags);
 
 	/* Free the excess tags when nr_hw_queues shrink. */
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index a2882751f0d2..e866875c17be 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -76,7 +76,7 @@  queue_requests_store(struct gendisk *disk, const char *page, size_t count)
 	if (ret < 0)
 		return ret;
 
-	memflags = blk_mq_freeze_queue(q);
+	memflags = blk_mq_enter_no_io_memsave(q);
 	mutex_lock(&q->elevator_lock);
 	if (nr < BLKDEV_MIN_RQ)
 		nr = BLKDEV_MIN_RQ;
@@ -85,7 +85,7 @@  queue_requests_store(struct gendisk *disk, const char *page, size_t count)
 	if (err)
 		ret = err;
 	mutex_unlock(&q->elevator_lock);
-	blk_mq_unfreeze_queue(q, memflags);
+	blk_mq_exit_no_io_memrestore(q, memflags);
 	return ret;
 }
 
@@ -592,7 +592,7 @@  static ssize_t queue_wb_lat_store(struct gendisk *disk, const char *page,
 	if (val < -1)
 		return -EINVAL;
 
-	memflags = blk_mq_freeze_queue(q);
+	memflags = blk_mq_enter_no_io_memsave(q);
 	mutex_lock(&q->elevator_lock);
 
 	rqos = wbt_rq_qos(q);
@@ -623,7 +623,7 @@  static ssize_t queue_wb_lat_store(struct gendisk *disk, const char *page,
 	blk_mq_unquiesce_queue(q);
 out:
 	mutex_unlock(&q->elevator_lock);
-	blk_mq_unfreeze_queue(q, memflags);
+	blk_mq_exit_no_io_memrestore(q, memflags);
 
 	return ret;
 }
diff --git a/block/elevator.c b/block/elevator.c
index 4d3a8f996c91..c9cb8386bf5e 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -724,13 +724,13 @@  ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
 
 	elv_iosched_load_module(name);
 
-	memflags = blk_mq_freeze_queue(q);
+	memflags = blk_mq_enter_no_io_memsave(q);
 	mutex_lock(&q->elevator_lock);
 	ret = elevator_change(q, name);
 	if (!ret)
 		ret = count;
 	mutex_unlock(&q->elevator_lock);
-	blk_mq_unfreeze_queue(q, memflags);
+	blk_mq_exit_no_io_memrestore(q, memflags);
 	return ret;
 }