[PATCH 5.8 317/633] mm/memcg: fix device private memcg accounting

[Greg Kroah-Hartman]

From: Ralph Campbell <rcampbell@xxxxxxxxxx>

[ Upstream commit 9a137153fc8798a89d8fce895cd0a06ea5b8e37c ]

The code in mc_handle_swap_pte() checks for non_swap_entry() and returns
NULL before checking is_device_private_entry() so device private pages are
never handled.  Fix this by checking for non_swap_entry() after handling
device private swap PTEs.

I assume the memory cgroup accounting would be off somehow when moving
a process to another memory cgroup.  Currently, the device private page
is charged like a normal anonymous page when allocated and is uncharged
when the page is freed so I think that path is OK.

Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Jerome Glisse <jglisse@xxxxxxxxxx>
Cc: Balbir Singh <bsingharora@xxxxxxxxx>
Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
Link: https://lkml.kernel.org/r/20201009215952.2726-1-rcampbell@xxxxxxxxxx
xFixes: c733a82874a7 ("mm/memcontrol: support MEMORY_DEVICE_PRIVATE")
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 mm/memcontrol.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 13f559af1ab6a..6795bdf662566 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5276,7 +5276,7 @@ static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
 	struct page *page = NULL;
 	swp_entry_t ent = pte_to_swp_entry(ptent);
 
-	if (!(mc.flags & MOVE_ANON) || non_swap_entry(ent))
+	if (!(mc.flags & MOVE_ANON))
 		return NULL;
 
 	/*
@@ -5295,6 +5295,9 @@ static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
 		return page;
 	}
 
+	if (non_swap_entry(ent))
+		return NULL;
+
 	/*
 	 * Because lookup_swap_cache() updates some statistics counter,
 	 * we call find_get_page() with swapper_space directly.
-- 
2.25.1