Re: [PATCH] ext4: free the new extent block when getting its buffer fails

[sashiko-bot@kernel.org]

> ext4_ext_grow_indepth() allocates and accounts a metadata block before
> calling sb_getblk_gfp(). If the buffer allocation fails, the new block
> has not been linked into the extent tree, but the error path returns
> without freeing it. This leaks the block and leaves i_blocks larger
> than the number of blocks reachable from the inode.
> 
> Commit 8a83ac54940d ("ext4: call bdev_getblk() from sb_getblk_gfp()")
> removed the implicit __GFP_NOFAIL from this allocation, making this
> error path reachable.
> 
> Free the new metadata block before returning -ENOMEM. Use
> ext4_free_blocks() to undo both the allocation and inode accounting.
> 
> Tested on Linux 6.12.1 by injecting a NULL result at the caller's buffer
> acquisition boundary. Before the fix, seven failed extent tree growth
> operations left seven allocated but unreachable blocks and i_blocks of
> 40 instead of 32 on a filesystem with 4 KiB blocks. After the fix, the
> same failures leave i_blocks at 32, and e2fsck -fn passes after a normal
> unmount. Retrying the operation, truncating the file, and growing the
> tree without injection also succeed.
> 
> Fixes: 8a83ac54940d ("ext4: call bdev_getblk() from sb_getblk_gfp()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Alan <3164729207@qq.com>

Sashiko has reviewed this patch and found no issues.

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