[PATCH 2/2] drm/shmem-helper: Avoid vm_open error paths

[Rob Clark]

From: Rob Clark <robdcl...@chromium.org>

vm_open() is not allowed to fail.  Fortunately we are guaranteed that
the pages are already pinned, and only need to increment the refcnt.  So
just increment it directly.

Fixes: 2194a63a818d ("drm: Add library for shmem backed GEM objects")
Cc: sta...@vger.kernel.org
Signed-off-by: Rob Clark <robdcl...@chromium.org>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c 
b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 110a9eac2af8..9885ba64127f 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -571,12 +571,20 @@ static void drm_gem_shmem_vm_open(struct vm_area_struct 
*vma)
 {
        struct drm_gem_object *obj = vma->vm_private_data;
        struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
-       int ret;
 
        WARN_ON(shmem->base.import_attach);
 
-       ret = drm_gem_shmem_get_pages(shmem);
-       WARN_ON_ONCE(ret != 0);
+       mutex_lock(&shmem->pages_lock);
+
+       /*
+        * We should have already pinned the pages, vm_open() just grabs
+        * an additional reference for the new mm the vma is getting
+        * copied into.
+        */
+       WARN_ON_ONCE(!shmem->pages_use_count);
+
+       shmem->pages_use_count++;
+       mutex_unlock(&shmem->pages_lock);
 
        drm_gem_vm_open(vma);
 }
-- 
2.38.1