drm/omap: fix race condition with dev->obj_list

omap_gem_objects are added to dev->obj_list in omap_gem_new, and removed
in omap_gem_free_object. Unfortunately there's no locking for
dev->obj_list, which eventually leads to a crash:

WARNING: CPU: 1 PID: 1123 at lib/list_debug.c:59 __list_del_entry+0xa4/0xe0()
list_del corruption. prev->next should be e9281344, but was ea722b84

Add a spinlock to protect dev->obj_list.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

3 files changed, 9 insertions, 0 deletions

diff --git a/drivers/gpu/drm/omapdrm/omap_drv.c b/drivers/gpu/drm/omapdrm/omap_drv.c
index c4c237317901..c6980985884b 100644
--- a/drivers/gpu/drm/omapdrm/omap_drv.c
+++ b/drivers/gpu/drm/omapdrm/omap_drv.c
@@ -491,6 +491,7 @@ static int dev_load(struct drm_device *dev, unsigned long flags)
 
         priv->wq = alloc_ordered_workqueue("omapdrm", 0);
 
+        spin_lock_init(&priv->list_lock);
         INIT_LIST_HEAD(&priv->obj_list);
 
         omap_gem_init(dev);
diff --git a/drivers/gpu/drm/omapdrm/omap_drv.h b/drivers/gpu/drm/omapdrm/omap_drv.h
index 57e11c1f589f..b31c79f15aed 100644
--- a/drivers/gpu/drm/omapdrm/omap_drv.h
+++ b/drivers/gpu/drm/omapdrm/omap_drv.h
@@ -105,6 +105,9 @@ struct omap_drm_private {
 
         struct workqueue_struct *wq;
 
+        /* lock for obj_list below */
+        spinlock_t 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 d37ee756a0b1..e9718b99a8a9 100644
--- a/drivers/gpu/drm/omapdrm/omap_gem.c
+++ b/drivers/gpu/drm/omapdrm/omap_gem.c
@@ -1273,13 +1273,16 @@ unlock:
 void omap_gem_free_object(struct drm_gem_object *obj)
 {
         struct drm_device *dev = obj->dev;
+        struct omap_drm_private *priv = dev->dev_private;
         struct omap_gem_object *omap_obj = to_omap_bo(obj);
 
         evict(obj);
 
         WARN_ON(!mutex_is_locked(&dev->struct_mutex));
 
+        spin_lock(&priv->list_lock);
         list_del(&omap_obj->mm_list);
+        spin_unlock(&priv->list_lock);
 
         drm_gem_free_mmap_offset(obj);
 
@@ -1377,7 +1380,9 @@ struct drm_gem_object *omap_gem_new(struct drm_device *dev,
         if (!omap_obj)
                 goto fail;
 
+        spin_lock(&priv->list_lock);
         list_add(&omap_obj->mm_list, &priv->obj_list);
+        spin_unlock(&priv->list_lock);
 
         obj = &omap_obj->base;