drm_gem_object_lookup_at_offset() can return a valid object with
filp or filp->f_op->get_unmapped_area set to NULL. Make sure we still
release the ref we acquired on such objects.

Cc: Loïc Molinari <[email protected]>
Fixes: 99bda20d6d4c ("drm/gem: Introduce drm_gem_get_unmapped_area() fop")
Signed-off-by: Boris Brezillon <[email protected]>
---
 drivers/gpu/drm/drm_gem.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 36c8af123877..f7cbf6e8d1e0 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -1298,11 +1298,13 @@ unsigned long drm_gem_get_unmapped_area(struct file 
*filp, unsigned long uaddr,
        unsigned long ret;
 
        obj = drm_gem_object_lookup_at_offset(filp, pgoff, len >> PAGE_SHIFT);
-       if (IS_ERR(obj) || !obj->filp || !obj->filp->f_op->get_unmapped_area)
-               return mm_get_unmapped_area(filp, uaddr, len, 0, flags);
+       if (IS_ERR(obj))
+               obj = NULL;
 
-       ret = obj->filp->f_op->get_unmapped_area(obj->filp, uaddr, len, 0,
-                                                flags);
+       if (!obj || !obj->filp || !obj->filp->f_op->get_unmapped_area)
+               ret = mm_get_unmapped_area(filp, uaddr, len, 0, flags);
+       else
+               ret = obj->filp->f_op->get_unmapped_area(obj->filp, uaddr, len, 
0, flags);
 
        drm_gem_object_put(obj);
 
-- 
2.52.0

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