Re: [PATCH v2 1/2] usb: offload: move device locking to callers in offload.c

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Mar 09, 2026 at 02:22:04AM +0000, Guan-Yu Lin wrote:
> Update usb_offload_get() and usb_offload_put() to require that the
> caller holds the USB device lock. Remove the internal call to
> usb_lock_device() and add device_lock_assert() to ensure synchronization
> is handled by the caller. These functions continue to manage the
> device's power state via autoresume/autosuspend and update the
> offload_usage counter.
> 
> Additionally, decouple the xHCI sideband interrupter lifecycle from the
> offload usage counter by removing the calls to usb_offload_get() and
> usb_offload_put() from the interrupter creation and removal paths. This
> allows interrupters to be managed independently of the device's offload
> activity status.
> 
> Cc: stable@vger.kernel.org
> Fixes: ef82a4803aab ("xhci: sideband: add api to trace sideband usage")
> Signed-off-by: Guan-Yu Lin <guanyulin@google.com>
> Tested-by: Hailong Liu <hailong.liu@oppo.com>
> ---
>  drivers/usb/core/offload.c       | 34 +++++++++++---------------------
>  drivers/usb/host/xhci-sideband.c | 14 +------------
>  2 files changed, 13 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/usb/core/offload.c b/drivers/usb/core/offload.c
> index 7c699f1b8d2b..e13a4c21d61b 100644
> --- a/drivers/usb/core/offload.c
> +++ b/drivers/usb/core/offload.c
> @@ -20,6 +20,7 @@
>   * enabled on this usb_device; that is, another entity is actively handling USB
>   * transfers. This information allows the USB driver to adjust its power
>   * management policy based on offload activity.
> + * The caller must hold @udev's device lock.

Ok, but:

>   *
>   * Return: 0 on success. A negative error code otherwise.
>   */
> @@ -27,31 +28,25 @@ int usb_offload_get(struct usb_device *udev)

Why are you not using the __must_hold() definition here?

>  {
>  	int ret;
>  
> -	usb_lock_device(udev);
> -	if (udev->state == USB_STATE_NOTATTACHED) {
> -		usb_unlock_device(udev);
> +	device_lock_assert(&udev->dev);

That's going to splat at runtime, not compile time, which is when you
really want to check for this, right?

And I thought all of the locking was messy before, and you cleaned it up
to be nicer here, why go back to the "old" way?  Having a caller be
forced to have a lock held is ripe for problems...

You also are not changing any callers to usb_offload_get() in this
patch, so does this leave the kernel tree in a broken state?  If not,
why not?  If so, that's not ok :(



> +
> +	if (udev->state == USB_STATE_NOTATTACHED)
>  		return -ENODEV;
> -	}
>  
>  	if (udev->state == USB_STATE_SUSPENDED ||
> -		   udev->offload_at_suspend) {
> -		usb_unlock_device(udev);
> +	    udev->offload_at_suspend)

Can't that really all be on one line?

>  		return -EBUSY;
> -	}
>  
>  	/*
>  	 * offload_usage could only be modified when the device is active, since
>  	 * it will alter the suspend flow of the device.
>  	 */
>  	ret = usb_autoresume_device(udev);
> -	if (ret < 0) {
> -		usb_unlock_device(udev);
> +	if (ret < 0)
>  		return ret;
> -	}
>  
>  	udev->offload_usage++;
>  	usb_autosuspend_device(udev);
> -	usb_unlock_device(udev);
>  
>  	return ret;
>  }
> @@ -64,6 +59,7 @@ EXPORT_SYMBOL_GPL(usb_offload_get);
>   * The inverse operation of usb_offload_get, which drops the offload_usage of
>   * a USB device. This information allows the USB driver to adjust its power
>   * management policy based on offload activity.
> + * The caller must hold @udev's device lock.
>   *
>   * Return: 0 on success. A negative error code otherwise.
>   */
> @@ -71,33 +67,27 @@ int usb_offload_put(struct usb_device *udev)

Again, use __must_hold() here, to catch build time issues.

And again, I don't see any code changes to reflect this new requirement
:(

thanks,

greg k-h