linux-kernel - [PATCH 4.14 89/95] drm/i915: Fix false-positive assert_rpm_wakelock_held in i915_pmic_bus_access

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Message-Id: <20171204160049.699763591@linuxfoundation.org>
Date:   Mon,  4 Dec 2017 17:00:53 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, FKr <bugs-freedesktop@...rmail.me>,
        Imre Deak <imre.deak@...el.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Jani Nikula <jani.nikula@...el.com>
Subject: [PATCH 4.14 89/95] drm/i915: Fix false-positive assert_rpm_wakelock_held in i915_pmic_bus_access_notifier v2

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Hans de Goede <j.w.r.degoede@...il.com>

commit f4359cedfb43b934f38c50d1604db21333abe57b upstream.

assert_rpm_wakelock_held is triggered from i915_pmic_bus_access_notifier
even though it gets unregistered on (runtime) suspend, this is caused
by a race happening under the following circumstances:

intel_runtime_pm_put does:

   atomic_dec(&dev_priv->pm.wakeref_count);

   pm_runtime_mark_last_busy(kdev);
   pm_runtime_put_autosuspend(kdev);

And pm_runtime_put_autosuspend calls intel_runtime_suspend from
a workqueue, so there is ample of time between the atomic_dec() and
intel_runtime_suspend() unregistering the notifier. If the notifier
gets called in this windowd assert_rpm_wakelock_held falsely triggers
(at this point we're not runtime-suspended yet).

This commit adds disable_rpm_wakeref_asserts and
enable_rpm_wakeref_asserts calls around the
intel_uncore_forcewake_get(FORCEWAKE_ALL) call in
i915_pmic_bus_access_notifier fixing the false-positive WARN_ON.

Changes in v2:
-Reword comment explaining why disabling the wakeref asserts is
 ok and necessary

Reported-by: FKr <bugs-freedesktop@...rmail.me>
Reviewed-by: Imre Deak <imre.deak@...el.com>
Signed-off-by: Hans de Goede <hdegoede@...hat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171110150301.9601-2-hdegoede@redhat.com
(cherry picked from commit ce30560c80dead91e98a03d90fb8791e57a9b69d)
Signed-off-by: Jani Nikula <jani.nikula@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/gpu/drm/i915/intel_uncore.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -1171,8 +1171,15 @@ static int i915_pmic_bus_access_notifier
 		 * bus, which will be busy after this notification, leading to:
 		 * "render: timed out waiting for forcewake ack request."
 		 * errors.
+		 *
+		 * The notifier is unregistered during intel_runtime_suspend(),
+		 * so it's ok to access the HW here without holding a RPM
+		 * wake reference -> disable wakeref asserts for the time of
+		 * the access.
 		 */
+		disable_rpm_wakeref_asserts(dev_priv);
 		intel_uncore_forcewake_get(dev_priv, FORCEWAKE_ALL);
+		enable_rpm_wakeref_asserts(dev_priv);
 		break;
 	case MBI_PMIC_BUS_ACCESS_END:
 		intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL);