[PATCH 5.4 35/66] drm/panfrost: Make sure the shrinker does not reclaim referenced BOs

[Greg Kroah-Hartman]

From: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>

commit 7e0cf7e9936c4358b0863357b90aa12afe6489da upstream.

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.

Fixes: 013b65101315 ("drm/panfrost: Add madvise and shrinker support")
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
Reviewed-by: Steven Price <steven.price@xxxxxxx>
Signed-off-by: Rob Herring <robh@xxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20191129135908.2439529-9-boris.brezillon@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/panfrost/panfrost_drv.c          |    1 +
 drivers/gpu/drm/panfrost/panfrost_gem.h          |    6 ++++++
 drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c |    3 +++
 drivers/gpu/drm/panfrost/panfrost_job.c          |    7 ++++++-
 4 files changed, 16 insertions(+), 1 deletion(-)

--- 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 *d
 			break;
 		}
 
+		atomic_inc(&bo->gpu_usecount);
 		job->mappings[i] = mapping;
 	}
 
--- 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;
 };
--- a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
+++ b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
@@ -41,6 +41,9 @@ static bool panfrost_gem_purge(struct dr
 	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;
 
--- 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
 	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);
 	}