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

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Message-ID: <2025102956-daunting-roping-a987@gregkh>
Date: Wed, 29 Oct 2025 13:51:19 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc: uttkarsh.aggarwal@....qualcomm.com, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org, mathias.nyman@...el.com,
	wesley.cheng@....qualcomm.com
Subject: Re: [RFT PATCH v3] xhci: sideband: Fix race condition in sideband
 unregister

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@oss.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>