SGT isn't refcounted. Once SGT pointer has been obtained, it remains the
same for both locked and unlocked get_pages_sgt(). Return cached SGT
directly without taking a potentially expensive lock.
Signed-off-by: Dmitry Osipenko <dmitry.osipe...@collabora.com>
---
drivers/gpu/drm/drm_gem_shmem_helper.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c
b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 8fd7851c088b..e6e6e693ab95 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -962,6 +962,18 @@ struct sg_table *drm_gem_shmem_get_pages_sgt(struct
drm_gem_shmem_object *shmem)
drm_WARN_ON(obj->dev, drm_gem_shmem_is_purgeable(shmem)))
return ERR_PTR(-EBUSY);
+ /*
+ * Drivers that use shrinker should take into account that shrinker
+ * may relocate BO, thus invalidating the returned SGT pointer.
+ * Such drivers should pin GEM while they use SGT.
+ *
+ * Drivers that don't use shrinker should take into account that
+ * SGT is released together with the GEM pages. Pages should be kept
+ * alive while SGT is used.
+ */
+ if (shmem->sgt)
+ return shmem->sgt;
+
ret = dma_resv_lock_interruptible(shmem->base.resv, NULL);
if (ret)
return ERR_PTR(ret);
--
2.43.0
