Re: [PATCH] loop: replace freezing queue with quiesce when changing loop specific setting

[Zhu Yanjun <yanjun.zhu@linux.dev>]

在 2025/4/3 12:54, Ming Lei 写道:
> freeze queue should be used for changing block layer generic setting, such
> as logical block size, PI, ..., and it is enough to quiesce queue for
> changing loop specific setting.
> 
> Remove the queue freeze warning in loop_update_dio(), since it is only
> needed in loop_set_block_size(), where queue is froze obviously.
> 
> Fix reported lockdep by syszbot:
> 
> https://lore.kernel.org/linux-block/67ea99e0.050a0220.3c3d88.0042.GAE@google.com/
> 
> Reported-by: syzbot+9dd7dbb1a4b915dee638@syzkaller.appspotmail.com
> Signed-off-by: Ming Lei <ming.lei@redhat.com>

I am fine with this commit.
Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>

Zhu Yanjun

> ---
>   drivers/block/loop.c | 14 +++++---------
>   1 file changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 674527d770dc..59886556f55c 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -190,8 +190,6 @@ static bool lo_can_use_dio(struct loop_device *lo)
>   static inline void loop_update_dio(struct loop_device *lo)
>   {
>   	lockdep_assert_held(&lo->lo_mutex);
> -	WARN_ON_ONCE(lo->lo_state == Lo_bound &&
> -		     lo->lo_queue->mq_freeze_depth == 0);
>   
>   	if ((lo->lo_flags & LO_FLAGS_DIRECT_IO) && !lo_can_use_dio(lo))
>   		lo->lo_flags &= ~LO_FLAGS_DIRECT_IO;
> @@ -595,7 +593,6 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
>   {
>   	struct file *file = fget(arg);
>   	struct file *old_file;
> -	unsigned int memflags;
>   	int error;
>   	bool partscan;
>   	bool is_loop;
> @@ -640,11 +637,11 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
>   
>   	/* and ... switch */
>   	disk_force_media_change(lo->lo_disk);
> -	memflags = blk_mq_freeze_queue(lo->lo_queue);
> +	blk_mq_quiesce_queue(lo->lo_queue);
>   	mapping_set_gfp_mask(old_file->f_mapping, lo->old_gfp_mask);
>   	loop_assign_backing_file(lo, file);
>   	loop_update_dio(lo);
> -	blk_mq_unfreeze_queue(lo->lo_queue, memflags);
> +	blk_mq_unquiesce_queue(lo->lo_queue);
>   	partscan = lo->lo_flags & LO_FLAGS_PARTSCAN;
>   	loop_global_unlock(lo, is_loop);
>   
> @@ -1270,7 +1267,6 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
>   	int err;
>   	bool partscan = false;
>   	bool size_changed = false;
> -	unsigned int memflags;
>   
>   	err = mutex_lock_killable(&lo->lo_mutex);
>   	if (err)
> @@ -1287,8 +1283,8 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
>   		invalidate_bdev(lo->lo_device);
>   	}
>   
> -	/* I/O needs to be drained before changing lo_offset or lo_sizelimit */
> -	memflags = blk_mq_freeze_queue(lo->lo_queue);
> +	/* queue needs to be quiesced before changing lo_offset or lo_sizelimit */
> +	blk_mq_quiesce_queue(lo->lo_queue);
>   
>   	err = loop_set_status_from_info(lo, info);
>   	if (err)
> @@ -1310,7 +1306,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
>   	loop_update_dio(lo);
>   
>   out_unfreeze:
> -	blk_mq_unfreeze_queue(lo->lo_queue, memflags);
> +	blk_mq_unquiesce_queue(lo->lo_queue);
>   	if (partscan)
>   		clear_bit(GD_SUPPRESS_PART_SCAN, &lo->lo_disk->state);
>   out_unlock: