btrfs: zoned: remove redundant space_info lock and variable in do_allocation_zoned()

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.

Reviewed-by: Boris Burkov <[email protected]>
Reviewed-by: Johannes Thumshirn <[email protected]>
Reviewed-by: Naohiro Aota <[email protected]>
Signed-off-by: Jiasheng Jiang <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Signed-off-by: David Sterba <[email protected]>

Author: Jiasheng Jiang

fs/btrfs/extent-tree.c

@@ -4013,9 +4013,8 @@ static int do_allocation_clustered(struct btrfs_block_group *block_group,
  * Lock nesting
  * ============
  *
- * space_info::lock
- *   block_group::lock
- *     fs_info::treelog_bg_lock
+ * block_group::lock
+ *   fs_info::treelog_bg_lock
  */
 
 /*
@@ -4028,7 +4027,6 @@ 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;
@@ -4089,7 +4087,6 @@ 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);
@@ -4191,7 +4188,6 @@ 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;
 }