[PATCH v4 03/40] drm/gem: Add ww_acquire_ctx support to drm_gem_lru_scan()

[Rob Clark <robdclark@gmail.com>]

From: Rob Clark <robdclark@chromium.org>

If the callback is going to have to attempt to grab more locks, it is
useful to have an ww_acquire_ctx to avoid locking order problems.

Why not use the drm_exec helper instead?  Mainly because (a) where
ww_acquire_init() is called is awkward, and (b) we don't really
need to retry after backoff, we can just move on to the next object.

Signed-off-by: Rob Clark <robdclark@chromium.org>
---
 drivers/gpu/drm/drm_gem.c              | 14 +++++++++++---
 drivers/gpu/drm/msm/msm_gem_shrinker.c | 24 +++++++++++++-----------
 include/drm/drm_gem.h                  | 10 ++++++----
 3 files changed, 30 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index ee811764c3df..9e3db9a864f8 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -1460,12 +1460,14 @@ EXPORT_SYMBOL(drm_gem_lru_move_tail);
  * @nr_to_scan: The number of pages to try to reclaim
  * @remaining: The number of pages left to reclaim, should be initialized by caller
  * @shrink: Callback to try to shrink/reclaim the object.
+ * @ticket: Optional ww_acquire_ctx context to use for locking
  */
 unsigned long
 drm_gem_lru_scan(struct drm_gem_lru *lru,
 		 unsigned int nr_to_scan,
 		 unsigned long *remaining,
-		 bool (*shrink)(struct drm_gem_object *obj))
+		 bool (*shrink)(struct drm_gem_object *obj, struct ww_acquire_ctx *ticket),
+		 struct ww_acquire_ctx *ticket)
 {
 	struct drm_gem_lru still_in_lru;
 	struct drm_gem_object *obj;
@@ -1498,17 +1500,20 @@ drm_gem_lru_scan(struct drm_gem_lru *lru,
 		 */
 		mutex_unlock(lru->lock);
 
+		if (ticket)
+			ww_acquire_init(ticket, &reservation_ww_class);
+
 		/*
 		 * Note that this still needs to be trylock, since we can
 		 * hit shrinker in response to trying to get backing pages
 		 * for this obj (ie. while it's lock is already held)
 		 */
-		if (!dma_resv_trylock(obj->resv)) {
+		if (!ww_mutex_trylock(&obj->resv->lock, ticket)) {
 			*remaining += obj->size >> PAGE_SHIFT;
 			goto tail;
 		}
 
-		if (shrink(obj)) {
+		if (shrink(obj, ticket)) {
 			freed += obj->size >> PAGE_SHIFT;
 
 			/*
@@ -1522,6 +1527,9 @@ drm_gem_lru_scan(struct drm_gem_lru *lru,
 
 		dma_resv_unlock(obj->resv);
 
+		if (ticket)
+			ww_acquire_fini(ticket);
+
 tail:
 		drm_gem_object_put(obj);
 		mutex_lock(lru->lock);
diff --git a/drivers/gpu/drm/msm/msm_gem_shrinker.c b/drivers/gpu/drm/msm/msm_gem_shrinker.c
index 07ca4ddfe4e3..de185fc34084 100644
--- a/drivers/gpu/drm/msm/msm_gem_shrinker.c
+++ b/drivers/gpu/drm/msm/msm_gem_shrinker.c
@@ -44,7 +44,7 @@ msm_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
 }
 
 static bool
-purge(struct drm_gem_object *obj)
+purge(struct drm_gem_object *obj, struct ww_acquire_ctx *ticket)
 {
 	if (!is_purgeable(to_msm_bo(obj)))
 		return false;
@@ -58,7 +58,7 @@ purge(struct drm_gem_object *obj)
 }
 
 static bool
-evict(struct drm_gem_object *obj)
+evict(struct drm_gem_object *obj, struct ww_acquire_ctx *ticket)
 {
 	if (is_unevictable(to_msm_bo(obj)))
 		return false;
@@ -79,21 +79,21 @@ wait_for_idle(struct drm_gem_object *obj)
 }
 
 static bool
-active_purge(struct drm_gem_object *obj)
+active_purge(struct drm_gem_object *obj, struct ww_acquire_ctx *ticket)
 {
 	if (!wait_for_idle(obj))
 		return false;
 
-	return purge(obj);
+	return purge(obj, ticket);
 }
 
 static bool
-active_evict(struct drm_gem_object *obj)
+active_evict(struct drm_gem_object *obj, struct ww_acquire_ctx *ticket)
 {
 	if (!wait_for_idle(obj))
 		return false;
 
-	return evict(obj);
+	return evict(obj, ticket);
 }
 
 static unsigned long
@@ -102,7 +102,7 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
 	struct msm_drm_private *priv = shrinker->private_data;
 	struct {
 		struct drm_gem_lru *lru;
-		bool (*shrink)(struct drm_gem_object *obj);
+		bool (*shrink)(struct drm_gem_object *obj, struct ww_acquire_ctx *ticket);
 		bool cond;
 		unsigned long freed;
 		unsigned long remaining;
@@ -122,8 +122,9 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
 			continue;
 		stages[i].freed =
 			drm_gem_lru_scan(stages[i].lru, nr,
-					&stages[i].remaining,
-					 stages[i].shrink);
+					 &stages[i].remaining,
+					 stages[i].shrink,
+					 NULL);
 		nr -= stages[i].freed;
 		freed += stages[i].freed;
 		remaining += stages[i].remaining;
@@ -164,7 +165,7 @@ msm_gem_shrinker_shrink(struct drm_device *dev, unsigned long nr_to_scan)
 static const int vmap_shrink_limit = 15;
 
 static bool
-vmap_shrink(struct drm_gem_object *obj)
+vmap_shrink(struct drm_gem_object *obj, struct ww_acquire_ctx *ticket)
 {
 	if (!is_vunmapable(to_msm_bo(obj)))
 		return false;
@@ -192,7 +193,8 @@ msm_gem_shrinker_vmap(struct notifier_block *nb, unsigned long event, void *ptr)
 		unmapped += drm_gem_lru_scan(lrus[idx],
 					     vmap_shrink_limit - unmapped,
 					     &remaining,
-					     vmap_shrink);
+					     vmap_shrink,
+					     NULL);
 	}
 
 	*(unsigned long *)ptr += unmapped;
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index fdae947682cd..0e2c476df731 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -555,10 +555,12 @@ void drm_gem_lru_init(struct drm_gem_lru *lru, struct mutex *lock);
 void drm_gem_lru_remove(struct drm_gem_object *obj);
 void drm_gem_lru_move_tail_locked(struct drm_gem_lru *lru, struct drm_gem_object *obj);
 void drm_gem_lru_move_tail(struct drm_gem_lru *lru, struct drm_gem_object *obj);
-unsigned long drm_gem_lru_scan(struct drm_gem_lru *lru,
-			       unsigned int nr_to_scan,
-			       unsigned long *remaining,
-			       bool (*shrink)(struct drm_gem_object *obj));
+unsigned long
+drm_gem_lru_scan(struct drm_gem_lru *lru,
+		 unsigned int nr_to_scan,
+		 unsigned long *remaining,
+		 bool (*shrink)(struct drm_gem_object *obj, struct ww_acquire_ctx *ticket),
+		 struct ww_acquire_ctx *ticket);
 
 int drm_gem_evict(struct drm_gem_object *obj);
 
-- 
2.49.0