[PATCH v2] drm/i915/userptr: Fix user pages leak on get_pages failure

[ZhaoJinming]

When ____i915_gem_object_get_pages() fails inside
i915_gem_object_userptr_submit_init(), the pvec containing pages
pinned by pin_user_pages_fast() was never freed:

1. obj->userptr.pvec was set to the pinned pages
2. The local pvec variable was NULLed
3. ____i915_gem_object_get_pages() failed, but its internal
   i915_gem_object_userptr_drop_ref() only decremented page_ref
   from 2 to 1, not triggering the pvec cleanup
4. The unconditional obj->userptr.page_ref-- brought page_ref
   to 0, but the pinned pages remained referenced only by
   obj->userptr.pvec with no path to reclaim them

Additionally, the cache hit path could return success on a
subsequent call despite page_ref being 0, leading to a
GEM_BUG_ON(obj->userptr.page_ref < 0) crash in drop_ref when
the pages were eventually invalidated.

Fix by calling i915_gem_object_userptr_drop_ref() on the
get_pages failure path, which properly decrements page_ref
from 1 to 0, triggering the pvec cleanup. Make the page_ref--
after the if block conditional on success, since drop_ref
already handles the refcount on failure.

Signed-off-by: ZhaoJinming <zhaojinming@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
index 043095f93ac6..7d2750528485 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
@@ -292,9 +292,12 @@ int i915_gem_object_userptr_submit_init(struct drm_i915_gem_object *obj)
 		obj->userptr.notifier_seq = notifier_seq;
 		pvec = NULL;
 		ret = ____i915_gem_object_get_pages(obj);
+		if (ret)
+			i915_gem_object_userptr_drop_ref(obj);
 	}
 
-	obj->userptr.page_ref--;
+	if (!ret)
+		obj->userptr.page_ref--;
 
 out_unlock:
 	i915_gem_object_unlock(obj);
-- 
2.20.1