Re: [PATCH v1 2/3] xfs/libxfs: replace kmalloc() and memcpy() with kmemdup()

[Darrick J. Wong]

On Tue, Dec 17, 2024 at 11:58:12PM +0100, Mirsad Todorovac wrote:
> The source static analysis tool gave the following advice:
> 
> ./fs/xfs/libxfs/xfs_dir2.c:382:15-22: WARNING opportunity for kmemdup
> 
>  → 382         args->value = kmalloc(len,
>    383                          GFP_KERNEL | __GFP_NOLOCKDEP | __GFP_RETRY_MAYFAIL);
>    384         if (!args->value)
>    385                 return -ENOMEM;
>    386
>  → 387         memcpy(args->value, name, len);
>    388         args->valuelen = len;
>    389         return -EEXIST;
> 
> Replacing kmalloc() + memcpy() with kmemdump() doesn't change semantics.
> Original code works without fault, so this is not a bug fix but proposed improvement.

I guess this is all right, but seeing as this code is shared with
userspace ("libxfs"), making this change will just add to the wrappers
that we have to have:

void *kmemdup_noprof(const void *src, size_t len, gfp_t gfp)
{
	void *p;

	p = kmalloc_node_track_caller_noprof(len, gfp, NUMA_NO_NODE, _RET_IP_);
	if (p)
		memcpy(p, src, len);
	return p;
}

Is this sufficiently better?  That's a question for the kernel
maintainer (cem) and the userspace maintainer (andrey, now cc'd).

--D

> Link: https://lwn.net/Articles/198928/
> Fixes: 94a69db2367ef ("xfs: use __GFP_NOLOCKDEP instead of GFP_NOFS")
> Fixes: 384f3ced07efd ("[XFS] Return case-insensitive match for dentry cache")
> Fixes: 2451337dd0439 ("xfs: global error sign conversion")
> Cc: Carlos Maiolino <cem@xxxxxxxxxx>
> Cc: "Darrick J. Wong" <djwong@xxxxxxxxxx>
> Cc: Chandan Babu R <chandanbabu@xxxxxxxxxx>
> Cc: Dave Chinner <dchinner@xxxxxxxxxx>
> Cc: linux-xfs@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: Mirsad Todorovac <mtodorovac69@xxxxxxxxx>
> ---
>  v1:
> 	initial version.
> 
>  fs/xfs/libxfs/xfs_dir2.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_dir2.c b/fs/xfs/libxfs/xfs_dir2.c
> index 202468223bf9..24251e42bdeb 100644
> --- a/fs/xfs/libxfs/xfs_dir2.c
> +++ b/fs/xfs/libxfs/xfs_dir2.c
> @@ -379,12 +379,11 @@ xfs_dir_cilookup_result(
>  					!(args->op_flags & XFS_DA_OP_CILOOKUP))
>  		return -EEXIST;
>  
> -	args->value = kmalloc(len,
> +	args->value = kmemdup(name, len,
>  			GFP_KERNEL | __GFP_NOLOCKDEP | __GFP_RETRY_MAYFAIL);
>  	if (!args->value)
>  		return -ENOMEM;
>  
> -	memcpy(args->value, name, len);
>  	args->valuelen = len;
>  	return -EEXIST;
>  }
> -- 
> 2.43.0
> 
>