linux-kernel - [PATCH] btrfs: zoned: remove redundant space_info lock and variable in do_allocation

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Message-Id: <20260112154040.35746-1-jiashengjiangcool@gmail.com>
Date: Mon, 12 Jan 2026 15:40:40 +0000
From: Jiasheng Jiang <jiashengjiangcool@...il.com>
To: Chris Mason <clm@...com>,
	David Sterba <dsterba@...e.com>,
	linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Jiasheng Jiang <jiashengjiangcool@...il.com>
Subject: [PATCH] btrfs: zoned: remove redundant space_info lock and variable in do_allocation_zoned

In do_allocation_zoned, the code acquires space_info->lock followed by
block_group->lock. However, the critical section does not access or
modify any members of the space_info structure, making the lock
acquisition and the space_info local variable redundant.

This unnecessary locking also creates a potential circular wait deadlock
(AB-BA) risk. Other paths, such as background reclaim or space reporting,
could acquire block_group->lock and subsequently attempt to acquire
space_info->lock to update global counters.

This behavior diverges from other Zoned-specific paths like
__btrfs_add_free_space_zoned which only rely on block_group->lock.
Removing the acquisition of space_info->lock and its corresponding
definition in do_allocation_zoned eliminates the deadlock risk and
improves concurrency by reducing contention on the global space_info lock.

Signed-off-by: Jiasheng Jiang <jiashengjiangcool@...il.com>
---
 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