On 2021/7/29 22:39, Shakeel Butt wrote:

On Thu, Jul 29, 2021 at 5:58 AM Miaohe Lin [off-list ref] wrote:

quoted

We should always ensure __mod_node_page_state() is called with preempt
disabled or percpu ops may manipulate the wrong cpu when preempt happened.

Fixes: b4e0b68fbd9d ("mm: memcontrol: use obj_cgroup APIs to charge kmem pages")
Signed-off-by: Miaohe Lin <redacted>
---
 mm/memcontrol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 70a32174e7c4..616d1a72ece3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

@@ -697,8 +697,8 @@ void __mod_lruvec_page_state(struct page *page, enum node_stat_item idx,
        memcg = page_memcg(head);
        /* Untracked pages have no memcg, no lruvec. Update only the node */
        if (!memcg) {
-               rcu_read_unlock();
                __mod_node_page_state(pgdat, idx, val);
+               rcu_read_unlock();

This rcu is for page_memcg. The preemption and interrupts are disabled
across __mod_lruvec_page_state().

I thought it's used to protect __mod_node_page_state(). Looks somewhat confusing for me.
Many thanks for pointing this out!

quoted

                return;
        }

--
2.23.0

.