Add lockless drm_gem_shmem_get_pages() helper that skips taking reservation
lock if pages_use_count is non-zero, leveraging from atomicity of the
refcount_t. Make drm_gem_shmem_mmap() to utilize the new helper.
Suggested-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
---
drivers/gpu/drm/drm_gem_shmem_helper.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index a0faef3e762d..d93ebfef20c7 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -227,6 +227,20 @@ void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
}
EXPORT_SYMBOL_GPL(drm_gem_shmem_put_pages_locked);
+static int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem)
+{
+ int ret;
+
+ if (refcount_inc_not_zero(&shmem->pages_use_count))
+ return 0;
+
+ dma_resv_lock(shmem->base.resv, NULL);
+ ret = drm_gem_shmem_get_pages_locked(shmem);
+ dma_resv_unlock(shmem->base.resv);
+
+ return ret;
+}
+
static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
{
int ret;
@@ -610,10 +624,7 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct
return ret;
}
- dma_resv_lock(shmem->base.resv, NULL);
- ret = drm_gem_shmem_get_pages_locked(shmem);
- dma_resv_unlock(shmem->base.resv);
-
+ ret = drm_gem_shmem_get_pages(shmem);
if (ret)
return ret;
--
2.41.0
