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

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

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