In cache_save_setup(), if create_free_space_inode() succeeds but the
subsequent lookup_free_space_inode() still fails on retry, the
BUG_ON(retries) will crash the kernel. This can happen due to I/O
errors or transient failures, not just programming bugs.

Replace the BUG_ON with proper error handling that returns the original
error code through the existing cleanup path. The callers already handle
this gracefully: disk_cache_state defaults to BTRFS_DC_ERROR, so the
space cache simply won't be written for that block group.

Signed-off-by: Teng Liu <27rabbitlt@gmail.com>
---
Changes in v2:
  - Use btrfs_err() instead of btrfs_debug() (Qu Wenruo)
  - Use PTR_ERR(inode) instead of hardcoded -EIO (Qu Wenruo)
  - Include error code in the log message (Qu Wenruo)

 fs/btrfs/block-group.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index ebf507909..89bfc9db0 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -3343,7 +3343,13 @@ static int cache_save_setup(struct btrfs_block_group *block_group,
 	}
 
 	if (IS_ERR(inode)) {
-		BUG_ON(retries);
+		if (retries) {
+			ret = PTR_ERR(inode);
+			btrfs_err(fs_info,
+				  "failed to lookup free space inode after creation for block group %llu: %d",
+				  block_group->start, ret);
+			goto out_free;
+		}
 		retries++;
 
 		if (block_group->ro)
-- 
2.53.0

在 2026/3/28 17:10, Teng Liu 写道:
> In cache_save_setup(), if create_free_space_inode() succeeds but the
> subsequent lookup_free_space_inode() still fails on retry, the
> BUG_ON(retries) will crash the kernel. This can happen due to I/O
> errors or transient failures, not just programming bugs.
> 
> Replace the BUG_ON with proper error handling that returns the original
> error code through the existing cleanup path. The callers already handle
> this gracefully: disk_cache_state defaults to BTRFS_DC_ERROR, so the
> space cache simply won't be written for that block group.
> 
> Signed-off-by: Teng Liu <27rabbitlt@gmail.com>

Reviewed-by: Qu Wenruo <wqu@suse.com>

And pushed to for-next.

> ---
> Changes in v2:
>    - Use btrfs_err() instead of btrfs_debug() (Qu Wenruo)
>    - Use PTR_ERR(inode) instead of hardcoded -EIO (Qu Wenruo)
>    - Include error code in the log message (Qu Wenruo)
> 
>   fs/btrfs/block-group.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
> index ebf507909..89bfc9db0 100644
> --- a/fs/btrfs/block-group.c
> +++ b/fs/btrfs/block-group.c
> @@ -3343,7 +3343,13 @@ static int cache_save_setup(struct btrfs_block_group *block_group,
>   	}
>   
>   	if (IS_ERR(inode)) {
> -		BUG_ON(retries);
> +		if (retries) {
> +			ret = PTR_ERR(inode);
> +			btrfs_err(fs_info,
> +				  "failed to lookup free space inode after creation for block group %llu: %d",
> +				  block_group->start, ret);
> +			goto out_free;
> +		}
>   		retries++;
>   
>   		if (block_group->ro)