Re: [PATCH v3] usb: hub: Set proper message when usb_hub_create_port_device() fails

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Oct 01, 2026 at 07:06:30PM +0800, Chen-Yu Tsai wrote:
> Right now when usb_hub_create_port_device() fails, it prints a separate
> error message to say which port failed, but otherwise leaves 'message'
> set to the default "out of memory", which is somewhat misleading.
> 
> Use a small buffer on the stack to put the custom formatted error message
> in and use it as the error message.
> 
> Assisted-by: LLM # local reviews
> Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
> ---
> Changes since v2:
> - Simplify to just using a small buffer on the stack (Alan)
> 
> Changes since v1:
> - Explicitly track and free the allocated custom error message instead
>   of using devm_kasprintf()
> - Link to v1:
>   https://lore.kernel.org/all/20260728100005.413868-1-wenst@chromium.org/
> 
> Sorry Andy, I ended up not using your __free(kfree_const) patch. My LLM
> was telling me that it won't work correctly if CONFIG_USB=m.
> ---
>  drivers/usb/core/hub.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 0e929a4c9fa1..d7f39e86b24c 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -1480,6 +1480,7 @@ static int hub_configure(struct usb_hub *hub,
>  	unsigned int pipe;
>  	int maxp, ret, i;
>  	char *message = "out of memory";
> +	char msg_buf[32] = {};

Why are you initializing this?

>  	unsigned unit_load;
>  	unsigned full_load;
>  	unsigned maxchild;
> @@ -1756,8 +1757,8 @@ static int hub_configure(struct usb_hub *hub,
>  	for (i = 0; i < maxchild; i++) {
>  		ret = usb_hub_create_port_device(hub, i + 1);
>  		if (ret < 0) {
> -			dev_err(hub->intfdev,
> -				"couldn't create port%d device.\n", i + 1);
> +			snprintf(msg_buf, sizeof(msg_buf), "couldn't create port%d device", i + 1);
> +			message = msg_buf;

Please just do what the other errors do, set message to something else
and leave the dev_err() here.  That way no extra stack space is needed.

And how did you hit this?

thanks,

greg k-h