Re: [PATCH] fwctl: mlx5: fix memory alloc/free in mlx5ctl_fw_rpc()

[Alison Schofield <alison.schofield@intel.com>]

On Sun, Aug 10, 2025 at 11:47:42PM +0530, Akhilesh Patil wrote:
> Use kvfree() to free memory allocated by kvzalloc() instead of kfree().
> Avoid potential memory management issue by matching alloc/free routines.
> 
> Fixes: 52929c2142041 ("fwctl/mlx5: Support for communicating with mlx5 fw")
> Signed-off-by: Akhilesh Patil <akhilesh@ee.iitb.ac.in>

Hi Akhilesh,

How about making the commit message more specific about why this
patch is critical even when no immediate symptoms are observed. Based
on the current description, a developer might think "this works fine
in my testing, so it's not urgent."

This type bug is particularly dangerous because it can pass code review
and testing, then cause mysterious production failures that are extremely
difficult to trace back to the root cause.

If this sounds like I'm going overboard on an obvious fix, I am doing
so intentionally. I am encouraging you, as a new contributor, to show
that you looked into how kvzalloc() works. I believe it can use either
kmalloc() or vmalloc(). You don't need to be a memory alloc expert to
submit this fix, but demonstrate that you looked beyond a report in a
static analysis tool. Also, that's where the interesting learnings
appear.

Similar to what Markus mentioned, a simple message stating how this
was found is useful too.

--Alison


> ---
>  drivers/fwctl/mlx5/main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/fwctl/mlx5/main.c b/drivers/fwctl/mlx5/main.c
> index f93aa0cecdb9..4b379f695eb7 100644
> --- a/drivers/fwctl/mlx5/main.c
> +++ b/drivers/fwctl/mlx5/main.c
> @@ -345,7 +345,7 @@ static void *mlx5ctl_fw_rpc(struct fwctl_uctx *uctx, enum fwctl_rpc_scope scope,
>  	 */
>  	if (ret && ret != -EREMOTEIO) {
>  		if (rpc_out != rpc_in)
> -			kfree(rpc_out);
> +			kvfree(rpc_out);
>  		return ERR_PTR(ret);
>  	}
>  	return rpc_out;
> -- 
> 2.34.1
>