linux-kernel - Re: [PATCH 3/3] drm/amdgpu: wire up the can

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Date: Fri, 2 Feb 2024 15:41:23 -0800
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Hamza Mahfooz <hamza.mahfooz@....com>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Alex Deucher <alexander.deucher@....com>,
	Christian König <christian.koenig@....com>,
	"Pan, Xinhui" <Xinhui.Pan@....com>,
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Mario Limonciello <mario.limonciello@....com>,
	Lijo Lazar <lijo.lazar@....com>,
	Srinivasan Shanmugam <srinivasan.shanmugam@....com>,
	Le Ma <le.ma@....com>,
	André Almeida <andrealmeid@...lia.com>,
	James Zhu <James.Zhu@....com>,
	Aurabindo Pillai <aurabindo.pillai@....com>,
	Alex Shi <alexs@...nel.org>, Jerry Snitselaar <jsnitsel@...hat.com>,
	Wei Liu <wei.liu@...nel.org>, Robin Murphy <robin.murphy@....com>,
	amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH 3/3] drm/amdgpu: wire up the can_remove() callback

On Fri, Feb 02, 2024 at 05:25:56PM -0500, Hamza Mahfooz wrote:
> Removing an amdgpu device that still has user space references allocated
> to it causes undefined behaviour. So, implement amdgpu_pci_can_remove()
> and disallow devices that still have files allocated to them from being
> unbound.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Hamza Mahfooz <hamza.mahfooz@....com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> index cc69005f5b46..cfa64f3c5be5 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> @@ -2323,6 +2323,22 @@ static int amdgpu_pci_probe(struct pci_dev *pdev,
>  	return ret;
>  }
>  
> +static bool amdgpu_pci_can_remove(struct pci_dev *pdev)
> +{
> +	struct drm_device *dev = pci_get_drvdata(pdev);
> +
> +	mutex_lock(&dev->filelist_mutex);
> +
> +	if (!list_empty(&dev->filelist)) {
> +		mutex_unlock(&dev->filelist_mutex);
> +		return false;
> +	}
> +
> +	mutex_unlock(&dev->filelist_mutex);
> +
> +	return true;

Also, to be pedantic, this will not work as right after you returned
"true" here, userspace could open a file, causing the same issue you are
trying to prevent to have happen, happen.

So even if we wanted to do this, which again, we do not, this isn't even
a solution for it because it will still cause you problems.

greg k-h