Re: [PATCH] drm/amdgpu: Disable RPM helpers while reprobing connectors on resume

[Alex Deucher <alexdeucher@gmail.com>]

On Fri, Jul 8, 2016 at 11:37 AM, Lyude <cpaul@redhat.com> wrote:
> Just about all of amdgpu's connector probing functions try to acquire
> runtime PM refs. If we try to do this in the context of
> amdgpu_resume_kms by calling drm_helper_hpd_irq_event(), we end up
> deadlocking the system.
>
> Since we're guaranteed to be holding the spinlock for RPM in
> amdgpu_resume_kms, and we already know the GPU is in working order, we
> need to prevent the RPM helpers from trying to run during the initial
> connector reprobe on resume.
>
> There's a couple of solutions I've explored for fixing this, but this
> one by far seems to be the simplest and most reliable (plus I'm pretty
> sure that's what disable_depth is there for anyway).
>
> Reproduction recipe:
>   - Get any laptop dual GPUs using PRIME
>   - Make sure runtime PM is enabled for amdgpu
>   - Boot the machine
>   - If the machine managed to boot without hanging, switch out of X to
>     another VT. This should definitely cause X to hang infinitely.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Lyude <cpaul@redhat.com>

Applied.  thanks!

Alex

> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> index 6e92008..46c1fee 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> @@ -1841,7 +1841,19 @@ int amdgpu_resume_kms(struct drm_device *dev, bool resume, bool fbcon)
>         }
>
>         drm_kms_helper_poll_enable(dev);
> +
> +       /*
> +        * Most of the connector probing functions try to acquire runtime pm
> +        * refs to ensure that the GPU is powered on when connector polling is
> +        * performed. Since we're calling this from a runtime PM callback,
> +        * trying to acquire rpm refs will cause us to deadlock.
> +        *
> +        * Since we're guaranteed to be holding the rpm lock, it's safe to
> +        * temporarily disable the rpm helpers so this doesn't deadlock us.
> +        */
> +       dev->dev->power.disable_depth++;
>         drm_helper_hpd_irq_event(dev);
> +       dev->dev->power.disable_depth--;
>
>         if (fbcon) {
>                 amdgpu_fbdev_set_suspend(adev, 0);
> --
> 2.7.4
>
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