Re: [PATCH v2] btrfs: zoned: remove redundant space_info lock and variable in do_allocation_zoned

[Boris Burkov <boris@bur.io>]

On Mon, Jan 12, 2026 at 08:22:27PM +0000, Jiasheng Jiang wrote:
> In do_allocation_zoned(), the code acquires space_info->lock before
> block_group->lock. However, the critical section does not access or
> modify any members of the space_info structure. Thus, the lock is
> redundant as it provides no necessary synchronization here.
> 
> This change simplifies the locking logic and aligns the function with
> other zoned paths, such as __btrfs_add_free_space_zoned(), which only
> rely on block_group->lock. Since the 'space_info' local variable is
> no longer used after removing the lock calls, it is also removed.
> 
> Removing this unnecessary lock reduces contention on the global
> space_info lock, improving concurrency in the zoned allocation path.
> 

It would probably be best if Johannes or Naohiro had a look at this,
just in case there is some space_info synchronization need I'm missing
(without accessing any fields like you pointed out) but I think it
looks correct.

Reviewed-by: Boris Burkov <boris@bur.io>

> Signed-off-by: Jiasheng Jiang <jiashengjiangcool@gmail.com>
> ---
> Changelog:
> 
> v1 -> v2:
> 
> 1. Removed the description about avoiding deadlocks.
> ---
>  fs/btrfs/extent-tree.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index e4cae34620d1..43d78056c274 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -3839,7 +3839,6 @@ static int do_allocation_zoned(struct btrfs_block_group *block_group,
>  			       struct btrfs_block_group **bg_ret)
>  {
>  	struct btrfs_fs_info *fs_info = block_group->fs_info;
> -	struct btrfs_space_info *space_info = block_group->space_info;
>  	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
>  	u64 start = block_group->start;
>  	u64 num_bytes = ffe_ctl->num_bytes;
> @@ -3900,7 +3899,6 @@ static int do_allocation_zoned(struct btrfs_block_group *block_group,
>  		 */
>  	}
>  
> -	spin_lock(&space_info->lock);
>  	spin_lock(&block_group->lock);
>  	spin_lock(&fs_info->treelog_bg_lock);
>  	spin_lock(&fs_info->relocation_bg_lock);
> @@ -4002,7 +4000,6 @@ static int do_allocation_zoned(struct btrfs_block_group *block_group,
>  	spin_unlock(&fs_info->relocation_bg_lock);
>  	spin_unlock(&fs_info->treelog_bg_lock);
>  	spin_unlock(&block_group->lock);
> -	spin_unlock(&space_info->lock);
>  	return ret;
>  }
>  
> -- 
> 2.25.1
>