Re: [PATCH] drm/amdgpu: add drm_dev_unplug() in GPU initialization failure to prevent crash

["Christian König" <christian.koenig@amd.com>]

Am 15.12.21 um 09:46 schrieb Leslie Shi:
> [Why]
> In amdgpu_driver_load_kms, when amdgpu_device_init returns error during driver modprobe, it
> will start the error handle path immediately and call into amdgpu_device_unmap_mmio as well
> to release mapped VRAM. However, in the following release callback, driver stills visits the
> unmapped memory like vcn.inst[i].fw_shared_cpu_addr in vcn_v3_0_sw_fini. So a kernel crash occurs.

Mhm, interesting workaround but I'm not sure that's the right thing to do.

Question is why are we unmapping the MMIO space on driver load failure 
so early in the first place? I mean don't we need to clean up a bit?

If that's really the way to go then we should at least add a comment 
explaining why it's done that way.

Regards,
Christian.

>
> [How]
> Add drm_dev_unplug() before executing amdgpu_driver_unload_kms to prevent such crash.
> GPU initialization failure is somehow allowed, but a kernel crash in this case should never happen.
>
> Signed-off-by: Leslie Shi <Yuliang.Shi@amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
> index 651c7abfde03..7bf6aecdbb92 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
> @@ -268,6 +268,8 @@ int amdgpu_driver_load_kms(struct amdgpu_device *adev, unsigned long flags)
>   		/* balance pm_runtime_get_sync in amdgpu_driver_unload_kms */
>   		if (adev->rmmio && adev->runpm)
>   			pm_runtime_put_noidle(dev->dev);
> +
> +		drm_dev_unplug(dev);
>   		amdgpu_driver_unload_kms(dev);
>   	}
>