linux-kernel - Re: [PATCH] drm/panthor: Fix race with suspend during unplug

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Message-ID: <cdb8495a-519e-469a-82e9-791094a81a52@arm.com>
Date: Wed, 22 Oct 2025 11:59:14 +0100
From: Steven Price <steven.price@....com>
To: Ketil Johnsen <ketil.johnsen@....com>,
 Boris Brezillon <boris.brezillon@...labora.com>,
 Liviu Dudau <liviu.dudau@....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>,
 Heiko Stuebner <heiko@...ech.de>
Cc: Grant Likely <grant.likely@...aro.org>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panthor: Fix race with suspend during unplug

On 22/10/2025 11:32, Ketil Johnsen wrote:
> There is a race between panthor_device_unplug() and
> panthor_device_suspend() which can lead to IRQ handlers running on a
> powered down GPU. This is how it can happen:
> - unplug routine calls drm_dev_unplug()
> - panthor_device_suspend() can now execute, and will skip a lot of
>   important work because the device is currently marked as unplugged.
> - IRQs will remain active in this case and IRQ handlers can therefore
>   try to access a powered down GPU.
> 
> The fix is simply to take the PM ref in panthor_device_unplug() a
> little bit earlier, before drm_dev_unplug().
> 
> Signed-off-by: Ketil Johnsen <ketil.johnsen@....com>
> Fixes: 5fe909cae118a ("drm/panthor: Add the device logical block")

Reviewed-by: Steven Price <steven.price@....com>

> ---
>  drivers/gpu/drm/panthor/panthor_device.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_device.c b/drivers/gpu/drm/panthor/panthor_device.c
> index 81df49880bd87..962a10e00848e 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.c
> +++ b/drivers/gpu/drm/panthor/panthor_device.c
> @@ -83,6 +83,8 @@ void panthor_device_unplug(struct panthor_device *ptdev)
>  		return;
>  	}
>  
> +	drm_WARN_ON(&ptdev->base, pm_runtime_get_sync(ptdev->base.dev) < 0);
> +
>  	/* Call drm_dev_unplug() so any access to HW blocks happening after
>  	 * that point get rejected.
>  	 */
> @@ -93,8 +95,6 @@ void panthor_device_unplug(struct panthor_device *ptdev)
>  	 */
>  	mutex_unlock(&ptdev->unplug.lock);
>  
> -	drm_WARN_ON(&ptdev->base, pm_runtime_get_sync(ptdev->base.dev) < 0);
> -
>  	/* Now, try to cleanly shutdown the GPU before the device resources
>  	 * get reclaimed.
>  	 */