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

Ming Lei
2025-04-02T04:39:57Z

Use blk_mq_no_io() 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: syzbot+4c7e0f9b94ad65811efb@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-block/67e6b425.050a0220.2f068f.007b.GAE@google.com/
Reported-by: Valdis Klētnieks <valdis.kletnieks@vt.edu>
Closes: https://lore.kernel.org/linux-block/7755.1743228130@turing-police/#t
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
block/blk-mq.c | 7 ++-----
block/blk-sysfs.c | 8 ++++----
block/elevator.c | 4 ++--
3 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 075ee51066b3..022d8139910d 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -4882,9 +4882,6 @@ 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;

@@ -5025,7 +5022,7 @@ 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
@@ -5074,7 +5071,7 @@ 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;
}

--
2.47.0