From: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Date: Fri, 4 Nov 2022 19:04:59 +0300
Subject: [PATCH] drm/msm/gem: Prevent blocking within shrinker loop
References: bsc#1012628
Patch-mainline: 6.2.8
Git-commit: 9630b585b607bd26f505d34620b14d75b9a5af7d

[ Upstream commit 9630b585b607bd26f505d34620b14d75b9a5af7d ]

Consider this scenario:

1. APP1 continuously creates lots of small GEMs
2. APP2 triggers `drop_caches`
3. Shrinker starts to evict APP1 GEMs, while APP1 produces new purgeable
   GEMs
4. msm_gem_shrinker_scan() returns non-zero number of freed pages
   and causes shrinker to try shrink more
5. msm_gem_shrinker_scan() returns non-zero number of freed pages again,
   goto 4
6. The APP2 is blocked in `drop_caches` until APP1 stops producing
   purgeable GEMs

To prevent this blocking scenario, check number of remaining pages
that GPU shrinker couldn't release due to a GEM locking contention
or shrinking rejection. If there are no remaining pages left to shrink,
then there is no need to free up more pages and shrinker may break out
from the loop.

This problem was found during shrinker/madvise IOCTL testing of
virtio-gpu driver. The MSM driver is affected in the same way.

Reviewed-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: b352ba54a820 ("drm/msm/gem: Convert to using drm_gem_lru")
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://lore.kernel.org/all/20230108210445.3948344-2-dmitry.osipenko@collabora.com/
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 drivers/gpu/drm/drm_gem.c              |  9 +++++++--
 drivers/gpu/drm/msm/msm_gem_shrinker.c | 11 +++++++++--
 include/drm/drm_gem.h                  |  4 +++-
 3 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index b8db675e..b0246a84 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -1375,10 +1375,13 @@ EXPORT_SYMBOL(drm_gem_lru_move_tail);
  *
  * @lru: The LRU to scan
  * @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.
  */
 unsigned long
-drm_gem_lru_scan(struct drm_gem_lru *lru, unsigned nr_to_scan,
+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 drm_gem_lru still_in_lru;
@@ -1417,8 +1420,10 @@ drm_gem_lru_scan(struct drm_gem_lru *lru, unsigned nr_to_scan,
 		 * 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 (!dma_resv_trylock(obj->resv)) {
+			*remaining += obj->size >> PAGE_SHIFT;
 			goto tail;
+		}
 
 		if (shrink(obj)) {
 			freed += obj->size >> PAGE_SHIFT;
diff --git a/drivers/gpu/drm/msm/msm_gem_shrinker.c b/drivers/gpu/drm/msm/msm_gem_shrinker.c
index 051bdbc0..f38296ad 100644
--- a/drivers/gpu/drm/msm/msm_gem_shrinker.c
+++ b/drivers/gpu/drm/msm/msm_gem_shrinker.c
@@ -107,6 +107,7 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
 		bool (*shrink)(struct drm_gem_object *obj);
 		bool cond;
 		unsigned long freed;
+		unsigned long remaining;
 	} stages[] = {
 		/* Stages of progressively more aggressive/expensive reclaim: */
 		{ &priv->lru.dontneed, purge,        true },
@@ -116,14 +117,18 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
 	};
 	long nr = sc->nr_to_scan;
 	unsigned long freed = 0;
+	unsigned long remaining = 0;
 
 	for (unsigned i = 0; (nr > 0) && (i < ARRAY_SIZE(stages)); i++) {
 		if (!stages[i].cond)
 			continue;
 		stages[i].freed =
-			drm_gem_lru_scan(stages[i].lru, nr, stages[i].shrink);
+			drm_gem_lru_scan(stages[i].lru, nr,
+					&stages[i].remaining,
+					 stages[i].shrink);
 		nr -= stages[i].freed;
 		freed += stages[i].freed;
+		remaining += stages[i].remaining;
 	}
 
 	if (freed) {
@@ -132,7 +137,7 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
 				     stages[3].freed);
 	}
 
-	return (freed > 0) ? freed : SHRINK_STOP;
+	return (freed > 0 && remaining > 0) ? freed : SHRINK_STOP;
 }
 
 #ifdef CONFIG_DEBUG_FS
@@ -182,10 +187,12 @@ msm_gem_shrinker_vmap(struct notifier_block *nb, unsigned long event, void *ptr)
 		NULL,
 	};
 	unsigned idx, unmapped = 0;
+	unsigned long remaining = 0;
 
 	for (idx = 0; lrus[idx] && unmapped < vmap_shrink_limit; idx++) {
 		unmapped += drm_gem_lru_scan(lrus[idx],
 					     vmap_shrink_limit - unmapped,
+					     &remaining,
 					     vmap_shrink);
 	}
 
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index a17c2f90..b46ade81 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -475,7 +475,9 @@ int drm_gem_dumb_map_offset(struct drm_file *file, struct drm_device *dev,
 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(struct drm_gem_lru *lru, struct drm_gem_object *obj);
-unsigned long drm_gem_lru_scan(struct drm_gem_lru *lru, unsigned nr_to_scan,
+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));
 
 #endif /* __DRM_GEM_H__ */
-- 
2.35.3