linux-kernel - Re: [PATCH v3 1/2] usb: udc: core: hide struct usb_gadget

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Date:   Sun, 20 Jun 2021 11:53:18 +0800
From:   linyyuan@...eaurora.org
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jack Pham <jackp@...eaurora.org>
Subject: Re: [PATCH v3 1/2] usb: udc: core: hide struct usb_gadget_driver to
 gadget driver

On 2021-06-20 11:46, linyyuan@...eaurora.org wrote:
> On 2021-06-20 10:13, Alan Stern wrote:
>> On Sat, Jun 19, 2021 at 11:43:08PM +0800, Linyu Yuan wrote:
>>> currently most gadget driver have a pointer to save
>>> struct usb_gadget_driver from upper layer,
>>> it allow upper layer set and unset of the pointer.
>>> 
>>> there is race that upper layer unset the pointer first,
>>> but gadget driver use the pointer later,
>>> and it cause system crash due to NULL pointer access.
>> 
>> This race has already been fixed in Greg's usb-next branch.  See 
>> commit
>> 7dc0c55e9f30 ("USB: UDC core: Add udc_async_callbacks gadget op") and
>> following commits 04145a03db9d ("USB: UDC: Implement
>> udc_async_callbacks in dummy-hcd") and b42e8090ba93 ("USB: UDC:
>> Implement udc_async_callbacks in net2280").
>> 
> thanks, this is better, lower driver only need change several places.
>> You just need to write a corresponding patch implementing the
>> async_callbacks op for dwc3.
> yes, i will do.
>> 
Alan, i want to discuss your suggestion again in b42e8090ba93 ("USB: 
UDC:
Implement udc_async_callbacks in net2280")

+                       if (dev->async_callbacks) { ----> if CPU1 saw 
this is true
+                               spin_unlock(&dev->lock); ---> CPU2 get 
lock after this unlock,
it will set async_callbacks to false, then follow call also crash, right 
?
+                               tmp = dev->driver->setup(&dev->gadget, 
&u.r);
+                               spin_lock(&dev->lock);
+                       }

>> Alan Stern