[PATCH v2 5/6] drm/omap: gem: Fix mm_list locking

[Laurent Pinchart]

From: Daniel Vetter <daniel.vetter at ffwll.ch>

- None of the list walkings where protected.

- Switch to a mutex since the list walking at device resume time can
  sleep when pinning buffers through the tiler.

Only thing we need to be careful with here is that while we walk the
list we can't unreference any gem objects, since the final unref would
result in a recursive deadlock. But the only functions that walk the
list is the device resume and debugfs dumping, so all safe.

Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen at ti.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
Changes since v1:

- Add done label for mutex unlocking in omap_gem_resume()
- Updated commit message to mention that the resume operation can sleep
---
 drivers/gpu/drm/omapdrm/omap_debugfs.c |  2 ++
 drivers/gpu/drm/omapdrm/omap_drv.c     |  2 +-
 drivers/gpu/drm/omapdrm/omap_drv.h     |  2 +-
 drivers/gpu/drm/omapdrm/omap_gem.c     | 15 +++++++++------
 4 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/omapdrm/omap_debugfs.c b/drivers/gpu/drm/omapdrm/omap_debugfs.c
index 95ade441caa8..91cf043f2b6b 100644
--- a/drivers/gpu/drm/omapdrm/omap_debugfs.c
+++ b/drivers/gpu/drm/omapdrm/omap_debugfs.c
@@ -32,7 +32,9 @@ static int gem_show(struct seq_file *m, void *arg)
 	struct omap_drm_private *priv = dev->dev_private;
 
 	seq_printf(m, "All Objects:\n");
+	mutex_lock(&priv->list_lock);
 	omap_gem_describe_objects(&priv->obj_list, m);
+	mutex_unlock(&priv->list_lock);
 
 	return 0;
 }
diff --git a/drivers/gpu/drm/omapdrm/omap_drv.c b/drivers/gpu/drm/omapdrm/omap_drv.c
index ef3b0e3571ec..5fcf9eaf3eaf 100644
--- a/drivers/gpu/drm/omapdrm/omap_drv.c
+++ b/drivers/gpu/drm/omapdrm/omap_drv.c
@@ -540,7 +540,7 @@ static int omapdrm_init(struct omap_drm_private *priv, struct device *dev)
 	priv->omaprev = soc ? (unsigned int)soc->data : 0;
 	priv->wq = alloc_ordered_workqueue("omapdrm", 0);
 
-	spin_lock_init(&priv->list_lock);
+	mutex_init(&priv->list_lock);
 	INIT_LIST_HEAD(&priv->obj_list);
 
 	/* Allocate and initialize the DRM device. */
diff --git a/drivers/gpu/drm/omapdrm/omap_drv.h b/drivers/gpu/drm/omapdrm/omap_drv.h
index 6eaee4df4559..f27c8e216adf 100644
--- a/drivers/gpu/drm/omapdrm/omap_drv.h
+++ b/drivers/gpu/drm/omapdrm/omap_drv.h
@@ -71,7 +71,7 @@ struct omap_drm_private {
 	struct workqueue_struct *wq;
 
 	/* lock for obj_list below */
-	spinlock_t list_lock;
+	struct mutex list_lock;
 
 	/* list of GEM objects: */
 	struct list_head obj_list;
diff --git a/drivers/gpu/drm/omapdrm/omap_gem.c b/drivers/gpu/drm/omapdrm/omap_gem.c
index 39cbc7273b29..5bccaf4d2d33 100644
--- a/drivers/gpu/drm/omapdrm/omap_gem.c
+++ b/drivers/gpu/drm/omapdrm/omap_gem.c
@@ -1005,6 +1005,7 @@ int omap_gem_resume(struct drm_device *dev)
 	struct omap_gem_object *omap_obj;
 	int ret = 0;
 
+	mutex_lock(&priv->list_lock);
 	list_for_each_entry(omap_obj, &priv->obj_list, mm_list) {
 		if (omap_obj->block) {
 			struct drm_gem_object *obj = &omap_obj->base;
@@ -1016,12 +1017,14 @@ int omap_gem_resume(struct drm_device *dev)
 					omap_obj->roll, true);
 			if (ret) {
 				dev_err(dev->dev, "could not repin: %d\n", ret);
-				return ret;
+				goto done;
 			}
 		}
 	}
 
-	return 0;
+done:
+	mutex_unlock(&priv->list_lock);
+	return ret;
 }
 #endif
 
@@ -1091,9 +1094,9 @@ void omap_gem_free_object(struct drm_gem_object *obj)
 
 	omap_gem_evict(obj);
 
-	spin_lock(&priv->list_lock);
+	mutex_lock(&priv->list_lock);
 	list_del(&omap_obj->mm_list);
-	spin_unlock(&priv->list_lock);
+	mutex_unlock(&priv->list_lock);
 
 	/*
 	 * No need to take the omap_obj.lock as at this point we own the sole
@@ -1218,9 +1221,9 @@ struct drm_gem_object *omap_gem_new(struct drm_device *dev,
 			goto err_release;
 	}
 
-	spin_lock(&priv->list_lock);
+	mutex_lock(&priv->list_lock);
 	list_add(&omap_obj->mm_list, &priv->obj_list);
-	spin_unlock(&priv->list_lock);
+	mutex_unlock(&priv->list_lock);
 
 	return obj;
 
-- 
Regards,

Laurent Pinchart