RE: [PATCH] usb: gadget: composite: unlock spinlock before usb_gadget_disconnect()

[David Laight <David.Laight@ACULAB.COM>]

From: Robert Baldyga
> usb_gadget_disconnect() shouldn't be called under spinlock to avoid
> spinlock recursion. Function usb_gadget_disconnect() calls pullup(),
> which is callback from UDC driver, usually calling composite_disconnect().
> This function wants to lock spinlock used in usb_function_deactivate()
> causing spinlock recursion.
...
> +++ b/drivers/usb/gadget/composite.c
> @@ -260,8 +260,11 @@ int usb_function_deactivate(struct usb_function *function)
> 
>  	spin_lock_irqsave(&cdev->lock, flags);
> 
> -	if (cdev->deactivations == 0)
> +	if (cdev->deactivations == 0) {
> +		spin_unlock_irqrestore(&cdev->lock, flags);
>  		status = usb_gadget_disconnect(cdev->gadget);
> +		spin_lock_irqsave(&cdev->lock, flags);
> +	}
>  	if (status == 0)
>  		cdev->deactivations++;

That sort of change rings big alarm bells.
You've effectively isolated the usb_gadget_disconnect() call
from the check that cdev->deactivations == 0.
And then you increment cdev->deactivations below.

Looks like it will be racy to me.

	David