linux-kernel - Re: [PATCH v2] usb: gadget: core: flush gadget workqueue after device removal

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Message-ID: <f083ad19-bea8-4a51-834c-14d6810699fe@rowland.harvard.edu>
Date: Wed, 5 Feb 2025 11:44:39 -0500
From: Alan Stern <stern@...land.harvard.edu>
To: Roy Luo <royluo@...gle.com>
Cc: Thinh.Nguyen@...opsys.com, gregkh@...uxfoundation.org,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	andre.draszik@...aro.org, elder@...nel.org, crwulff@...il.com,
	paul@...pouillou.net, jkeeping@...usicbrands.com,
	yuanlinyu@...onor.com, sumit.garg@...aro.org, balbi@...com,
	stable@...r.kernel.org
Subject: Re: [PATCH v2] usb: gadget: core: flush gadget workqueue after
 device removal

On Tue, Feb 04, 2025 at 11:36:42PM +0000, Roy Luo wrote:
> device_del() can lead to new work being scheduled in gadget->work
> workqueue. This is observed, for example, with the dwc3 driver with the
> following call stack:
>   device_del()
>     gadget_unbind_driver()
>       usb_gadget_disconnect_locked()
>         dwc3_gadget_pullup()
> 	  dwc3_gadget_soft_disconnect()
> 	    usb_gadget_set_state()
> 	      schedule_work(&gadget->work)
> 
> Move flush_work() after device_del() to ensure the workqueue is cleaned
> up.
> 
> Fixes: 5702f75375aa9 ("usb: gadget: udc-core: move sysfs_notify() to a workqueue")
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Roy Luo <royluo@...gle.com>
> ---

Reviewed-by: Alan Stern <stern@...land.harvard.edu>

>  drivers/usb/gadget/udc/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
> index a6f46364be65..4b3d5075621a 100644
> --- a/drivers/usb/gadget/udc/core.c
> +++ b/drivers/usb/gadget/udc/core.c
> @@ -1543,8 +1543,8 @@ void usb_del_gadget(struct usb_gadget *gadget)
>  
>  	kobject_uevent(&udc->dev.kobj, KOBJ_REMOVE);
>  	sysfs_remove_link(&udc->dev.kobj, "gadget");
> -	flush_work(&gadget->work);
>  	device_del(&gadget->dev);
> +	flush_work(&gadget->work);
>  	ida_free(&gadget_id_numbers, gadget->id_number);
>  	cancel_work_sync(&udc->vbus_work);
>  	device_unregister(&udc->dev);
> 
> base-commit: f286757b644c226b6b31779da95a4fa7ab245ef5
> -- 
> 2.48.1.362.g079036d154-goog
>