Re: [RFT PATCH v3] xhci: sideband: Fix race condition in sideband unregister

[Mathias Nyman <mathias.nyman@linux.intel.com>]

On 11/7/25 08:16, Uttkarsh Aggarwal wrote:
> 
> 
> On 10/29/2025 7:22 PM, Mathias Nyman wrote:
>> On 10/29/25 14:51, Greg KH wrote:
>>> On Wed, Oct 29, 2025 at 02:24:35PM +0200, Mathias Nyman wrote:
>>>> Uttkarsh Aggarwal observed a kernel panic during sideband un-register
>>>> and found it was caused by a race condition between sideband unregister,
>>>> and creating sideband interrupters.
>>>> The issue occurrs when thread T1 runs uaudio_disconnect() and released
>>>> sb->xhci via sideband_unregister, while thread T2 simultaneously accessed
>>>> the now-NULL sb->xhci in xhci_sideband_create_interrupter() resulting in
>>>> a crash.
>>>>
>>>> Ensure new endpoints or interrupter can't be added to a sidenband after
>>>> xhci_sideband_unregister() cleared the existing ones, and unlocked the
>>>> sideband mutex.
>>>> Reorganize code so that mutex is only taken and released once in
>>>> xhci_sideband_unregister(), and clear sb->vdev while mutex is taken.
>>>>
>>>> Use mutex guards to reduce human unlock errors in code
>>>>
>>>> Refuse to add endpoints or interrupter if sb->vdev is not set.
>>>> sb->vdev is set when sideband is created and registered.
>>>>
>>>> Reported-by: Uttkarsh Aggarwal <uttkarsh.aggarwal@oss.qualcomm.com>
>>>> Closes: https://lore.kernel.org/linux-usb/20251028080043.27760-1- uttkarsh.aggarwal@oss.qualcomm.com
>>>> Fixes: de66754e9f80 ("xhci: sideband: add initial api to register a secondary interrupter entity")
>>>> Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
>>>> ---
>>>
>>> Looks good, thanks for respinning this.  I don't know if it fixes the
>>> issue, but it looks sane :)
>>>
>>> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>
>> Thanks for reviewing this.
>>
>> I don't have the hardware to test this myself either
>>
>> Thanks
>> Mathias
> 
> Hi Mathias,
> 
> I have shared the patch with our OEMs and so far, have not received any reports of issues from them.
> 
> Thanks
> Uttkarsh
> 

Thanks, I'll send it forward

-Mathias