Patch "drm/i915: Fix races on fbdev" has been added to the 4.5-stable tree

From a7442b93cf32c1e1ddb721a26cd1f92302e2a222 Mon Sep 17 00:00:00 2001

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

drm/i915: Fix races on fbdev

to the 4.5-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-i915-fix-races-on-fbdev.patch

and it can be found in the queue-4.5 subdirectory.

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

From a7442b93cf32c1e1ddb721a26cd1f92302e2a222 Mon Sep 17 00:00:00 2001
From: Lukas Wunner <[email protected]>
Date: Wed, 9 Mar 2016 12:52:53 +0100
Subject: drm/i915: Fix races on fbdev
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From: Lukas Wunner <[email protected]>

commit a7442b93cf32c1e1ddb721a26cd1f92302e2a222 upstream.

The ->lastclose callback invokes intel_fbdev_restore_mode() and has been witnessed to run before intel_fbdev_initial_config_async() has finished.

We might likewise receive hotplug events before we've had a chance to fully set up the fbdev.

Fix by waiting for the asynchronous thread to finish.

v2:
An async_synchronize_full() was also added to intel_fbdev_set_suspend() in v1 which turned out to be entirely gratuitous. It caused a deadlock on suspend (discovered by CI, thanks to Damien Lespiau and Tomi Sarvela for CI support) and was unnecessary since a device is never suspended until its ->probe callback (and all asynchronous tasks it scheduled) have finished. See dpm_prepare(), which calls wait_for_device_probe(), which calls async_synchronize_full().

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93580

Reported-by Gustav F�gerlind <[email protected]>

Reported-by "Li, Weinan Z" <[email protected]>

Cc Chris Wilson <[email protected]>

Signed-off-by Lukas Wunner <[email protected]>

Signed-off-by Daniel Vetter <[email protected]>

Link http://patchwork.freedesktop.org/patch/msgid/[email protected]

Signed-off-by Greg Kroah-Hartman <[email protected]>

---
 drivers/gpu/drm/i915/i915_dma.c    |    8 +++-----
 drivers/gpu/drm/i915/intel_fbdev.c |    3 +++
 2 files changed, 6 insertions(+), 5 deletions(-)

drivers/gpu/drm/i915/i915_dma.c +3 -5

@@ -437,11 +437,9 @@ static int i915_load_modeset_init(struct
 	 * Some ports require correctly set-up hpd registers for detection to
 	 * work properly (leading to ghost connected connector status), e.g. VGA
 	 * on gm45.  Hence we can only set up the initial fbdev config after hpd
-	 * irqs are fully enabled. Now we should scan for the initial config
-	 * only once hotplug handling is enabled, but due to screwed-up locking
-	 * around kms/fbdev init we can't protect the fdbev initial config
-	 * scanning against hotplug events. Hence do this first and ignore the
-	 * tiny window where we will loose hotplug notifactions.
+	 * irqs are fully enabled. We protect the fbdev initial config scanning
+	 * against hotplug events by waiting in intel_fbdev_output_poll_changed
+	 * until the asynchronous thread has finished.
 	 */
 	intel_fbdev_initial_config_async(dev);
 

drivers/gpu/drm/i915/intel_fbdev.c +3 -0

@@ -797,6 +797,8 @@ void intel_fbdev_set_suspend(struct drm_
 void intel_fbdev_output_poll_changed(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	async_synchronize_full();
 	if (dev_priv->fbdev)
 		drm_fb_helper_hotplug_event(&dev_priv->fbdev->helper);
 }

@@ -808,6 +810,7 @@ void intel_fbdev_restore_mode(struct drm
 	struct intel_fbdev *ifbdev = dev_priv->fbdev;
 	struct drm_fb_helper *fb_helper;
 
+	async_synchronize_full();
 	if (!ifbdev)
 		return;
 

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

queue-4.5/drm-i915-fix-races-on-fbdev.patch

Quoted 8 lines · On Sat, Jun 04, 2016 at 02:22:34PM -0700, [email protected] wrote:

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

drm/i915: Fix races on fbdev

to the 4.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

Quoted 6 lines

The filename of the patch is:

     drm-i915-fix-races-on-fbdev.patch

and it can be found in the queue-4.5 subdirectory.

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

That patch unfortunately turned out to cause deadlocks on suspend/resume on ILK, SNB and IVB in Intel's CI test farm (which I couldn't reproduce on my IVB machine and therefore couldn't debug). The commit was reverted upstream with 934458c2c95d.

Therefore please do not apply it to stable kernels. My apologies for the inconvenience.