[PATCH] HID: wacom: use GFP_ATOMIC in wacom_wac_queue_flush()

[PATCH] HID: wacom: use GFP_ATOMIC in wacom_wac_queue_flush()

[Jinmo Yang]

wacom_wac_queue_flush() is called via the .raw_event callback
(wacom_raw_event → wacom_wac_pen_serial_enforce → wacom_wac_queue_flush).
For USB HID devices, this callback is invoked from hid_irq_in(), which
is a URB completion handler running in atomic context. Using GFP_KERNEL
in this path can sleep, leading to a "scheduling while atomic" bug.

Use GFP_ATOMIC instead. The existing code already handles allocation
failure by skipping the fifo entry and continuing.

Suggested-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Fixes: 5e013ad20689 ("HID: wacom: Remove static WACOM_PKGLEN_MAX limit")
Cc: stable@vger.kernel.org
Signed-off-by: Jinmo Yang <jinmo44.yang@gmail.com>
---
 drivers/hid/wacom_sys.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hid/wacom_sys.c b/drivers/hid/wacom_sys.c
index a32320b35..2e237bdd2 100644
--- a/drivers/hid/wacom_sys.c
+++ b/drivers/hid/wacom_sys.c
@@ -74,7 +74,7 @@ static void wacom_wac_queue_flush(struct hid_device *hdev,
 		unsigned int count;
 		int err;
 
-		buf = kzalloc(size, GFP_KERNEL);
+		buf = kzalloc(size, GFP_ATOMIC);
 		if (!buf) {
 			kfifo_skip(fifo);
 			continue;
-- 
2.53.0

Re: [PATCH] HID: wacom: use GFP_ATOMIC in wacom_wac_queue_flush()

[Dmitry Torokhov]

Hi Jinmo,

On Sun, May 31, 2026 at 12:59:30AM +0900, Jinmo Yang wrote:
> wacom_wac_queue_flush() is called via the .raw_event callback
> (wacom_raw_event → wacom_wac_pen_serial_enforce → wacom_wac_queue_flush).
> For USB HID devices, this callback is invoked from hid_irq_in(), which
> is a URB completion handler running in atomic context. Using GFP_KERNEL
> in this path can sleep, leading to a "scheduling while atomic" bug.
> 
> Use GFP_ATOMIC instead. The existing code already handles allocation
> failure by skipping the fifo entry and continuing.
> 
> Suggested-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

If you want to give credit this should be "Reported-by: Sashiko-bot <...>".

> Fixes: 5e013ad20689 ("HID: wacom: Remove static WACOM_PKGLEN_MAX limit")
> Cc: stable@vger.kernel.org
> Signed-off-by: Jinmo Yang <jinmo44.yang@gmail.com>
> ---
>  drivers/hid/wacom_sys.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/hid/wacom_sys.c b/drivers/hid/wacom_sys.c
> index a32320b35..2e237bdd2 100644
> --- a/drivers/hid/wacom_sys.c
> +++ b/drivers/hid/wacom_sys.c
> @@ -74,7 +74,7 @@ static void wacom_wac_queue_flush(struct hid_device *hdev,
>  		unsigned int count;
>  		int err;
>  
> -		buf = kzalloc(size, GFP_KERNEL);
> +		buf = kzalloc(size, GFP_ATOMIC);
>  		if (!buf) {
>  			kfifo_skip(fifo);
>  			continue;

Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

As a followup please consider changing 'buf' management to use cleanup
facilities:

		u8 *buf __free(kfree) = kzalloc(size, GFP_ATOMIC);
		if (!buf) {
			kfifo_skiip(fifo);
			continue;
		}
		...

Thanks.

-- 
Dmitry