linux-kernel - [PATCH] drm/i915/pmu: avoid -Wmaybe-uninitialized warning

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Date:   Tue, 13 Mar 2018 13:08:29 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Michal Wajdeczko <michal.wajdeczko@...el.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] drm/i915/pmu: avoid -Wmaybe-uninitialized warning

The conditional spinlock confuses gcc into thinking the 'flags' value
might contain uninitialized data:

drivers/gpu/drm/i915/i915_pmu.c: In function '__i915_pmu_event_read':
arch/x86/include/asm/paravirt_types.h:573:3: error: 'flags' may be used uninitialized in this function [-Werror=maybe-uninitialized]

The code is correct, but it's easy to see how the compiler gets confused
here. This avoids the problem by pulling the lock outside of the function
into its only caller.

Fixes: 1fe699e30113 ("drm/i915/pmu: Fix sleep under atomic in RC6 readout")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/gpu/drm/i915/i915_pmu.c | 25 ++++++++++---------------
 1 file changed, 10 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
index 4bc7aefa9541..2c8c705d1f18 100644
--- a/drivers/gpu/drm/i915/i915_pmu.c
+++ b/drivers/gpu/drm/i915/i915_pmu.c
@@ -415,7 +415,6 @@ static u64 __get_rc6(struct drm_i915_private *i915)
 static u64 get_rc6(struct drm_i915_private *i915, bool locked)
 {
 #if IS_ENABLED(CONFIG_PM)
-	unsigned long flags;
 	u64 val;
 
 	if (intel_runtime_pm_get_if_in_use(i915)) {
@@ -428,18 +427,12 @@ static u64 get_rc6(struct drm_i915_private *i915, bool locked)
 		 * previously.
 		 */
 
-		if (!locked)
-			spin_lock_irqsave(&i915->pmu.lock, flags);
-
 		if (val >= i915->pmu.sample[__I915_SAMPLE_RC6_ESTIMATED].cur) {
 			i915->pmu.sample[__I915_SAMPLE_RC6_ESTIMATED].cur = 0;
 			i915->pmu.sample[__I915_SAMPLE_RC6].cur = val;
 		} else {
 			val = i915->pmu.sample[__I915_SAMPLE_RC6_ESTIMATED].cur;
 		}
-
-		if (!locked)
-			spin_unlock_irqrestore(&i915->pmu.lock, flags);
 	} else {
 		struct pci_dev *pdev = i915->drm.pdev;
 		struct device *kdev = &pdev->dev;
@@ -452,9 +445,6 @@ static u64 get_rc6(struct drm_i915_private *i915, bool locked)
 		 * on top of the last known real value, as the approximated RC6
 		 * counter value.
 		 */
-		if (!locked)
-			spin_lock_irqsave(&i915->pmu.lock, flags);
-
 		spin_lock_irqsave(&kdev->power.lock, flags2);
 
 		if (!i915->pmu.sample[__I915_SAMPLE_RC6_ESTIMATED].cur)
@@ -470,9 +460,6 @@ static u64 get_rc6(struct drm_i915_private *i915, bool locked)
 		val = jiffies_to_nsecs(val);
 		val += i915->pmu.sample[__I915_SAMPLE_RC6].cur;
 		i915->pmu.sample[__I915_SAMPLE_RC6_ESTIMATED].cur = val;
-
-		if (!locked)
-			spin_unlock_irqrestore(&i915->pmu.lock, flags);
 	}
 
 	return val;
@@ -519,8 +506,16 @@ static u64 __i915_pmu_event_read(struct perf_event *event, bool locked)
 			val = count_interrupts(i915);
 			break;
 		case I915_PMU_RC6_RESIDENCY:
-			val = get_rc6(i915, locked);
-			break;
+			if (!locked) {
+				unsigned long flags;
+
+				spin_lock_irqsave(&i915->pmu.lock, flags);
+				val = get_rc6(i915, locked);
+				spin_unlock_irqrestore(&i915->pmu.lock, flags);
+				break;
+			} else {
+				val = get_rc6(i915, locked);
+			}
 		}
 	}
 
-- 
2.9.0