Re: [PATCH 8/8] drm/panfrost: Make sure the shrinker does not reclaim referenced BOs

On 29/11/2019 1:59 pm, Boris Brezillon wrote:

Userspace might tag a BO purgeable while it's still referenced by GPU jobs. We need to make sure the shrinker does not purge such BOs until all jobs referencing it are finished.

Nit: for extra robustness, perhaps it's worth using the refcount_t API rather than bare atomic_t?

Robin.

Fixes: 013b65101315 ("drm/panfrost: Add madvise and shrinker support") Cc: stable@vger.kernel.org Signed-off-by: Boris Brezillon boris.brezillon@collabora.com

---

drivers/gpu/drm/panfrost/panfrost_drv.c | 1 + drivers/gpu/drm/panfrost/panfrost_gem.h | 6 ++++++ drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c | 2 ++ drivers/gpu/drm/panfrost/panfrost_job.c | 7 ++++++- 4 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c index b406b5243b40..297c0e7304d2 100644 --- a/drivers/gpu/drm/panfrost/panfrost_drv.c +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c @@ -166,6 +166,7 @@ panfrost_lookup_bos(struct drm_device *dev, break; }

• atomic_inc(&bo->gpu_usecount);
  

  job->mappings[i] = mapping; }

diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.h b/drivers/gpu/drm/panfrost/panfrost_gem.h index ca1bc9019600..b3517ff9630c 100644 --- a/drivers/gpu/drm/panfrost/panfrost_gem.h +++ b/drivers/gpu/drm/panfrost/panfrost_gem.h @@ -30,6 +30,12 @@ struct panfrost_gem_object { struct mutex lock; } mappings;

• /*

• * Count the number of jobs referencing this BO so we don't let the
  

• * shrinker reclaim this object prematurely.
  

• */
  

• atomic_t gpu_usecount;
• bool noexec :1; bool is_heap :1; };

diff --git a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c index b36df326c860..288e46c40673 100644 --- a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c +++ b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c @@ -41,6 +41,8 @@ static bool panfrost_gem_purge(struct drm_gem_object *obj) struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj); struct panfrost_gem_object *bo = to_panfrost_bo(obj);

• if (atomic_read(&bo->gpu_usecount))

• return false;
  

if (!mutex_trylock(&shmem->pages_lock)) return false; diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c index c85d45be3b5e..2b12aa87ff32 100644 --- a/drivers/gpu/drm/panfrost/panfrost_job.c +++ b/drivers/gpu/drm/panfrost/panfrost_job.c @@ -270,8 +270,13 @@ static void panfrost_job_cleanup(struct kref *ref) dma_fence_put(job->render_done_fence); if (job->mappings) {

• for (i = 0; i < job->bo_count; i++)
  

• for (i = 0; i < job->bo_count; i++) {
  

• 	if (!job->mappings[i])
  

• 		break;
  

• 	atomic_dec(&job->mappings[i]->obj->gpu_usecount);
  panfrost_gem_mapping_put(job->mappings[i]);
  

• }
  

  kvfree(job->mappings); }