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

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Message-ID: <22d15a74-f04f-413a-966f-9581739e4c5a@oss.qualcomm.com>
Date: Fri, 7 Nov 2025 11:46:15 +0530
From: Uttkarsh Aggarwal <uttkarsh.aggarwal@....qualcomm.com>
To: Mathias Nyman <mathias.nyman@...el.com>,
        Greg KH <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        wesley.cheng@....qualcomm.com
Subject: Re: [RFT PATCH v3] xhci: sideband: Fix race condition in sideband
 unregister



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@....qualcomm.com>
>>> Closes: https://lore.kernel.org/linux-usb/20251028080043.27760-1- 
>>> uttkarsh.aggarwal@....qualcomm.com
>>> Fixes: de66754e9f80 ("xhci: sideband: add initial api to register a 
>>> secondary interrupter entity")
>>> Signed-off-by: Mathias Nyman <mathias.nyman@...ux.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@...uxfoundation.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