Hi Am 08.01.23 um 22:04 schrieb Dmitry Osipenko:
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@xxxxxxxxx> Fixes: b352ba54a820 ("drm/msm/gem: Convert to using drm_gem_lru") Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> --- drivers/gpu/drm/drm_gem.c | 9 +++++++-- drivers/gpu/drm/msm/msm_gem_shrinker.c | 8 ++++++-- include/drm/drm_gem.h | 4 +++- 3 files changed, 16 insertions(+), 5 deletions(-) diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c index 59a0bb5ebd85..c6bca5ac6e0f 100644 --- a/drivers/gpu/drm/drm_gem.c +++ b/drivers/gpu/drm/drm_gem.c @@ -1388,10 +1388,13 @@ 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 * @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; @@ -1430,8 +1433,10 @@ 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 051bdbc093cf..b7c1242014ec 100644 --- a/drivers/gpu/drm/msm/msm_gem_shrinker.c +++ b/drivers/gpu/drm/msm/msm_gem_shrinker.c @@ -116,12 +116,14 @@ 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, &remaining,
This function relies in remaining being pre-initialized. That's not obvious and error prone. At least, pass-in something like &stages[i].remaining that is then initialized internally by drm_gem_lru_scan() to zero. And similar to freed, sum up the individual stages' remaining here.
TBH I somehow don't like the overall design of how all these functions interact with each other. But I also can't really point to the actual problem. So it's best to take what you have here; maybe with the change I proposed.
Reviewed-by: Thomas Zimmermann <tzimmermann@xxxxxxx> Best regards Thomas
+ stages[i].shrink); nr -= stages[i].freed; freed += stages[i].freed; } @@ -132,7 +134,7 @@ 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 +184,12 @@ 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.hindex 772a4adf5287..f1f00fc2dba6 100644 --- a/include/drm/drm_gem.h +++ b/include/drm/drm_gem.h @@ -476,7 +476,9 @@ 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__ */
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Ivo Totev
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