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Date: Fri, 2 Feb 2024 16:41:02 -0600
From: Bjorn Helgaas <helgaas@kernel.org>
To: Hamza Mahfooz <hamza.mahfooz@amd.com>
Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Alex Deucher <alexander.deucher@amd.com>,
	Christian =?utf-8?B?S8O2bmln?= <christian.koenig@amd.com>,
	"Pan, Xinhui" <Xinhui.Pan@amd.com>,
	David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Mario Limonciello <mario.limonciello@amd.com>,
	Lijo Lazar <lijo.lazar@amd.com>,
	Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>,
	Le Ma <le.ma@amd.com>,
	=?utf-8?B?QW5kcsOp?= Almeida <andrealmeid@igalia.com>,
	James Zhu <James.Zhu@amd.com>,
	Aurabindo Pillai <aurabindo.pillai@amd.com>,
	Alex Shi <alexs@kernel.org>, Jerry Snitselaar <jsnitsel@redhat.com>,
	Wei Liu <wei.liu@kernel.org>, Robin Murphy <robin.murphy@arm.com>,
	amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	linux-pci@vger.kernel.org, Bartosz Golaszewski <brgl@bgdev.pl>
Subject: Re: [PATCH 3/3] drm/amdgpu: wire up the can_remove() callback
Message-ID: <20240202224102.GA732304@bhelgaas>
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In-Reply-To: <20240202222603.141240-3-hamza.mahfooz@amd.com>

[+cc Bartosz]

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.

Maybe this would help for things that are completely built-in or
soldered down, but nothing can prevent a user from physically pulling
a card or cable, so I don't think this is a generic solution to the
problem of dangling user space references.

Maybe Bartosz's recent LPC talk is relevant:
https://lpc.events/event/17/contributions/1627/

> Cc: stable@vger.kernel.org
> Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.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;
> +}
> +
>  static void
>  amdgpu_pci_remove(struct pci_dev *pdev)
>  {
> @@ -2929,6 +2945,7 @@ static struct pci_driver amdgpu_kms_pci_driver = {
>  	.name = DRIVER_NAME,
>  	.id_table = pciidlist,
>  	.probe = amdgpu_pci_probe,
> +	.can_remove = amdgpu_pci_can_remove,
>  	.remove = amdgpu_pci_remove,
>  	.shutdown = amdgpu_pci_shutdown,
>  	.driver.pm = &amdgpu_pm_ops,
> -- 
> 2.43.0
>