Patch "drm/amdgpu: Disable RPM helpers while reprobing connectors on resume" has been added to the 4.7-stable tree

This is a note to let you know that I've just added the patch titled

drm/amdgpu: Disable RPM helpers while reprobing connectors on resume

to the 4.7-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drm-amdgpu-disable-rpm-helpers-while-reprobing-connectors-on-resume.patch
and it can be found in the queue-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Lyude <[email protected]>
Date: Mon, 18 Jul 2016 11:41:37 -0400
Subject: drm/amdgpu: Disable RPM helpers while reprobing connectors on resume

From: Lyude <[email protected]>

commit 23a1a9e54e71593fe5657e883662995d181d2d6b upstream.

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

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

@@ -1841,7 +1841,23 @@ int amdgpu_resume_kms(struct drm_device
 	}
 
 	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);

Patches currently in stable-queue which might be from [email protected] are

queue-4.7/drm-amdgpu-poll-for-both-connect-disconnect-on-analog-connectors.patch queue-4.7/drm-radeon-poll-for-both-connect-disconnect-on-analog-connectors.patch queue-4.7/drm-amdgpu-disable-rpm-helpers-while-reprobing-connectors-on-resume.patch