[PATCH 12/14] drm/msm: drop struct_mutex in madvise path

[Rob Clark]

From: Rob Clark <robdclark at chromium.org>

The obj->lock is sufficient for what we need.

This *does* have the implication that userspace can try to shoot
themselves in the foot by racing madvise(DONTNEED) with submit.  But
the result will be about the same if they did madvise(DONTNEED) before
the submit ioctl, ie. they might not get want they want if they race
with shrinker.  But iova fault handling is robust enough, and userspace
is only shooting it's own foot.

Signed-off-by: Rob Clark <robdclark at chromium.org>
---
 drivers/gpu/drm/msm/msm_drv.c          | 11 ++------
 drivers/gpu/drm/msm/msm_gem.c          |  6 ++--
 drivers/gpu/drm/msm/msm_gem.h          | 38 ++++++++++++++++++--------
 drivers/gpu/drm/msm/msm_gem_shrinker.c |  4 +--
 4 files changed, 32 insertions(+), 27 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
index e766c1f45045..d2488816ce48 100644
--- a/drivers/gpu/drm/msm/msm_drv.c
+++ b/drivers/gpu/drm/msm/msm_drv.c
@@ -906,14 +906,9 @@ static int msm_ioctl_gem_madvise(struct drm_device *dev, void *data,
 		return -EINVAL;
 	}
 
-	ret = mutex_lock_interruptible(&dev->struct_mutex);
-	if (ret)
-		return ret;
-
 	obj = drm_gem_object_lookup(file, args->handle);
 	if (!obj) {
-		ret = -ENOENT;
-		goto unlock;
+		return -ENOENT;
 	}
 
 	ret = msm_gem_madvise(obj, args->madv);
@@ -922,10 +917,8 @@ static int msm_ioctl_gem_madvise(struct drm_device *dev, void *data,
 		ret = 0;
 	}
 
-	drm_gem_object_put_locked(obj);
+	drm_gem_object_put(obj);
 
-unlock:
-	mutex_unlock(&dev->struct_mutex);
 	return ret;
 }
 
diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index 5e75d644ce41..9cdac4f7228c 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -639,8 +639,6 @@ int msm_gem_madvise(struct drm_gem_object *obj, unsigned madv)
 
 	mutex_lock(&msm_obj->lock);
 
-	WARN_ON(!mutex_is_locked(&obj->dev->struct_mutex));
-
 	if (msm_obj->madv != __MSM_MADV_PURGED)
 		msm_obj->madv = madv;
 
@@ -657,7 +655,7 @@ void msm_gem_purge(struct drm_gem_object *obj, enum msm_gem_lock subclass)
 	struct msm_gem_object *msm_obj = to_msm_bo(obj);
 
 	WARN_ON(!mutex_is_locked(&dev->struct_mutex));
-	WARN_ON(!is_purgeable(msm_obj));
+	WARN_ON(!is_purgeable(msm_obj, subclass));
 	WARN_ON(obj->import_attach);
 
 	mutex_lock_nested(&msm_obj->lock, subclass);
@@ -749,7 +747,7 @@ void msm_gem_active_get(struct drm_gem_object *obj, struct msm_gpu *gpu)
 	struct msm_drm_private *priv = obj->dev->dev_private;
 
 	might_sleep();
-	WARN_ON(msm_obj->madv != MSM_MADV_WILLNEED);
+	WARN_ON(msm_gem_madv(msm_obj, OBJ_LOCK_NORMAL) != MSM_MADV_WILLNEED);
 
 	if (!atomic_fetch_inc(&msm_obj->active_count)) {
 		mutex_lock(&priv->mm_lock);
diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h
index e98a8004813b..bb8aa6b1b254 100644
--- a/drivers/gpu/drm/msm/msm_gem.h
+++ b/drivers/gpu/drm/msm/msm_gem.h
@@ -97,18 +97,6 @@ static inline bool is_active(struct msm_gem_object *msm_obj)
 	return atomic_read(&msm_obj->active_count);
 }
 
-static inline bool is_purgeable(struct msm_gem_object *msm_obj)
-{
-	WARN_ON(!mutex_is_locked(&msm_obj->base.dev->struct_mutex));
-	return (msm_obj->madv == MSM_MADV_DONTNEED) && msm_obj->sgt &&
-			!msm_obj->base.dma_buf && !msm_obj->base.import_attach;
-}
-
-static inline bool is_vunmapable(struct msm_gem_object *msm_obj)
-{
-	return (msm_obj->vmap_count == 0) && msm_obj->vaddr;
-}
-
 /* The shrinker can be triggered while we hold objA->lock, and need
  * to grab objB->lock to purge it.  Lockdep just sees these as a single
  * class of lock, so we use subclasses to teach it the difference.
@@ -125,6 +113,32 @@ enum msm_gem_lock {
 	OBJ_LOCK_SHRINKER,
 };
 
+/* Use this helper to read msm_obj->madv when msm_obj->lock not held: */
+static inline unsigned
+msm_gem_madv(struct msm_gem_object *msm_obj, enum msm_gem_lock subclass)
+{
+	unsigned madv;
+
+	mutex_lock_nested(&msm_obj->lock, subclass);
+	madv = msm_obj->madv;
+	mutex_unlock(&msm_obj->lock);
+
+	return madv;
+}
+
+static inline bool
+is_purgeable(struct msm_gem_object *msm_obj, enum msm_gem_lock subclass)
+{
+	return (msm_gem_madv(msm_obj, subclass) == MSM_MADV_DONTNEED) &&
+			msm_obj->sgt && !msm_obj->base.dma_buf &&
+			!msm_obj->base.import_attach;
+}
+
+static inline bool is_vunmapable(struct msm_gem_object *msm_obj)
+{
+	return (msm_obj->vmap_count == 0) && msm_obj->vaddr;
+}
+
 void msm_gem_purge(struct drm_gem_object *obj, enum msm_gem_lock subclass);
 void msm_gem_vunmap(struct drm_gem_object *obj, enum msm_gem_lock subclass);
 
diff --git a/drivers/gpu/drm/msm/msm_gem_shrinker.c b/drivers/gpu/drm/msm/msm_gem_shrinker.c
index c41b84a3a484..39a1b5327267 100644
--- a/drivers/gpu/drm/msm/msm_gem_shrinker.c
+++ b/drivers/gpu/drm/msm/msm_gem_shrinker.c
@@ -54,7 +54,7 @@ msm_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
 	mutex_lock(&priv->mm_lock);
 
 	list_for_each_entry(msm_obj, &priv->inactive_list, mm_list) {
-		if (is_purgeable(msm_obj))
+		if (is_purgeable(msm_obj, OBJ_LOCK_SHRINKER))
 			count += msm_obj->base.size >> PAGE_SHIFT;
 	}
 
@@ -84,7 +84,7 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
 	list_for_each_entry(msm_obj, &priv->inactive_list, mm_list) {
 		if (freed >= sc->nr_to_scan)
 			break;
-		if (is_purgeable(msm_obj)) {
+		if (is_purgeable(msm_obj, OBJ_LOCK_SHRINKER)) {
 			msm_gem_purge(&msm_obj->base, OBJ_LOCK_SHRINKER);
 			freed += msm_obj->base.size >> PAGE_SHIFT;
 		}
-- 
2.26.2