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Subject[PATCH v15 14/23] drm/shmem-helper: Add and use lockless drm_gem_shmem_get_pages()
Date
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 kref
counter. Make drm_gem_shmem_mmap() to utilize the new helper.

Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
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 5a2e37b3e51d..f386289c24fc 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -234,6 +234,20 @@ 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 (kref_get_unless_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;
@@ -616,10 +630,7 @@ 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
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