On Mon, Jul 18, 2016 at 11:41 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.

Changes since v1:

• add appropriate #ifdef checks for CONFIG_PM. This is not very useful, but it appears some kernel test suites test compiling amdgpu with CONFIG_PM disabled, which results in this patch breaking the builds if we don't include this #ifdef

Cc: stable@vger.kernel.org Cc: Alex Deucher alexdeucher@gmail.com Signed-off-by: Lyude cpaul@redhat.com

Applied. Thanks!

Alex

---

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c index 6e92008..b7f5650 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c @@ -1841,7 +1841,23 @@ 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.
  

•    */
  

+#ifdef CONFIG_PM

•   dev->dev->power.disable_depth++;
  

+#endif drm_helper_hpd_irq_event(dev); +#ifdef CONFIG_PM

•   dev->dev->power.disable_depth--;
  

+#endif

    if (fbcon) {
            amdgpu_fbdev_set_suspend(adev, 0);

-- 2.7.4