linux-kernel - [PATCH] drm/msm/atomic: Drop per-CRTC locks in reverse order

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Message-Id: <20201020222600.264876-1-robdclark@gmail.com>
Date:   Tue, 20 Oct 2020 15:26:00 -0700
From:   Rob Clark <robdclark@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     Krishna Manikandan <mkrishn@...eaurora.org>,
        Rob Clark <robdclark@...omium.org>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        linux-arm-msm@...r.kernel.org (open list:DRM DRIVER FOR MSM ADRENO GPU),
        freedreno@...ts.freedesktop.org (open list:DRM DRIVER FOR MSM ADRENO
        GPU), linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] drm/msm/atomic: Drop per-CRTC locks in reverse order

From: Rob Clark <robdclark@...omium.org>

lockdep dislikes seeing locks unwound in a non-nested fashion.

Fixes: 37c2016e3608 ("drm/msm: Fix race condition in msm driver with async layer updates")
Signed-off-by: Rob Clark <robdclark@...omium.org>
---
 drivers/gpu/drm/msm/msm_atomic.c |  2 +-
 drivers/gpu/drm/msm/msm_kms.h    |  4 ++++
 include/drm/drm_crtc.h           | 10 ++++++++++
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/msm_atomic.c b/drivers/gpu/drm/msm/msm_atomic.c
index b03d6ab6b19b..6a326761dc4a 100644
--- a/drivers/gpu/drm/msm/msm_atomic.c
+++ b/drivers/gpu/drm/msm/msm_atomic.c
@@ -67,7 +67,7 @@ static void unlock_crtcs(struct msm_kms *kms, unsigned int crtc_mask)
 {
 	struct drm_crtc *crtc;
 
-	for_each_crtc_mask(kms->dev, crtc, crtc_mask)
+	for_each_crtc_mask_reverse(kms->dev, crtc, crtc_mask)
 		mutex_unlock(&kms->commit_lock[drm_crtc_index(crtc)]);
 }
 
diff --git a/drivers/gpu/drm/msm/msm_kms.h b/drivers/gpu/drm/msm/msm_kms.h
index 8d3e626c9fee..d8151a89e163 100644
--- a/drivers/gpu/drm/msm/msm_kms.h
+++ b/drivers/gpu/drm/msm/msm_kms.h
@@ -211,4 +211,8 @@ int dpu_mdss_init(struct drm_device *dev);
 	drm_for_each_crtc(crtc, dev) \
 		for_each_if (drm_crtc_mask(crtc) & (crtc_mask))
 
+#define for_each_crtc_mask_reverse(dev, crtc, crtc_mask) \
+	drm_for_each_crtc_reverse(crtc, dev) \
+		for_each_if (drm_crtc_mask(crtc) & (crtc_mask))
+
 #endif /* __MSM_KMS_H__ */
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index dfdb04619b0d..25f5958f2882 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -1274,4 +1274,14 @@ static inline struct drm_crtc *drm_crtc_find(struct drm_device *dev,
 #define drm_for_each_crtc(crtc, dev) \
 	list_for_each_entry(crtc, &(dev)->mode_config.crtc_list, head)
 
+/**
+ * drm_for_each_crtc_reverse - iterate over all CRTCs in reverse order
+ * @crtc: a &struct drm_crtc as the loop cursor
+ * @dev: the &struct drm_device
+ *
+ * Iterate over all CRTCs of @dev.
+ */
+#define drm_for_each_crtc_reverse(crtc, dev) \
+	list_for_each_entry_reverse(crtc, &(dev)->mode_config.crtc_list, head)
+
 #endif /* __DRM_CRTC_H__ */
-- 
2.26.2