linux-kernel - Re: [PATCH] drm/panthor: Fix NULL pointer dereference on panthor_fw

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Message-ID: <fc3fb243-48fb-4a5a-8802-01a7fe5ef032@arm.com>
Date: Mon, 19 Jan 2026 08:18:11 +0000
From: Steven Price <steven.price@....com>
To: Andy Yan <andyshrk@....com>, Liviu Dudau <liviu.dudau@....com>
Cc: Karunika Choo <karunika.choo@....com>, dri-devel@...ts.freedesktop.org,
 nd@....com, Boris Brezillon <boris.brezillon@...labora.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 linux-kernel@...r.kernel.org, aishwarya.tcv@....com
Subject: Re: [PATCH] drm/panthor: Fix NULL pointer dereference on
 panthor_fw_unplug

On 19/01/2026 06:33, Andy Yan wrote:
> 
> Hello,
> 
> At 2025-12-16 20:51:53, "Liviu Dudau" <liviu.dudau@....com> wrote:
>> On Mon, Dec 15, 2025 at 08:33:12PM +0000, Karunika Choo wrote:
>>> This patch removes the MCU halt and wait for halt procedures during
>>> panthor_fw_unplug() as the MCU can be in a variety of states or the FW
>>> may not even be loaded/initialized at all, the latter of which can lead
>>> to a NULL pointer dereference.
>>>
>>> It should be safe on unplug to just disable the MCU without waiting for
>>> it to halt as it may not be able to.
>>>
>>> Fixes: 514072549865 ("drm/panthor: Support GLB_REQ.STATE field for Mali-G1 GPUs")
>>> Suggested-by: Boris Brezillon <boris.brezillon@...labora.com>
>>> Signed-off-by: Karunika Choo <karunika.choo@....com>
>>
>> Reviewed-by: Liviu Dudau <liviu@...au.co.uk>
> 
>   Tested-by: Andy Yan <andyshrk@....com>
> 
> Hope can be merged in 6.19 release cycle.

Boris has already merged this:

commit 920c6af98e98e6afedf6318a75bac95af8415c6c
Author: Karunika Choo <karunika.choo@....com>
Date:   Mon Dec 15 20:33:12 2025 +0000

    drm/panthor: Fix NULL pointer dereference on panthor_fw_unplug

However it's in the drm-misc-next branch which means it won't be pulled
until the merge window. Ideally it would have gone in via
drm-misc-fixes, but given this (AFAIK) only triggers in the combination
of loading the panthor driver *and* not having the correct firmware I
didn't think it was worth worrying about - and so haven't asked the DRM
maintainers to cherry pick it. The fix should get backported into a
6.19.x stable release.

If I've missed something then let me (and the DRM maintainers) know and
the commit can be cherry-picked.

Thanks,
Steve

> 
>>
>> Best regards,
>> Liviu
>>
>>> ---
>>>  drivers/gpu/drm/panthor/panthor_fw.c | 4 ----
>>>  1 file changed, 4 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/panthor/panthor_fw.c b/drivers/gpu/drm/panthor/panthor_fw.c
>>> index 4beaa589ba66..a64ec8756bed 100644
>>> --- a/drivers/gpu/drm/panthor/panthor_fw.c
>>> +++ b/drivers/gpu/drm/panthor/panthor_fw.c
>>> @@ -1261,10 +1261,6 @@ void panthor_fw_unplug(struct panthor_device *ptdev)
>>>  		if (ptdev->fw->irq.irq)
>>>  			panthor_job_irq_suspend(&ptdev->fw->irq);
>>>  
>>> -		panthor_fw_halt_mcu(ptdev);
>>> -		if (!panthor_fw_wait_mcu_halted(ptdev))
>>> -			drm_warn(&ptdev->base, "Failed to halt MCU on unplug");
>>> -
>>>  		panthor_fw_stop(ptdev);
>>>  	}
>>>  
>>> -- 
>>> 2.49.0
>>>