FAILED: patch "[PATCH] mm/memcontrol: fix data-race on reading jiffies_64" failed to apply to 6.6-stable tree

FAILED: patch "[PATCH] mm/memcontrol: fix data-race on reading jiffies_64" failed to apply to 6.6-stable tree

[Sasha Levin]

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x c20cf1c3c8cdd98618d6fcc794003a0e003ae858
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107053200-failed-6.6-c20cf1c3c8cd@kernel.org' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From c20cf1c3c8cdd98618d6fcc794003a0e003ae858 Mon Sep 17 00:00:00 2001
From: Jiayuan Chen <jiayuan.chen@linux.dev>
Date: Thu, 27 Aug 2026 10:54:56 +0800
Subject: [PATCH] mm/memcontrol: fix data-race on reading jiffies_64

KCSAN reported a data-race between tick_do_update_jiffies64() updating
jiffies_64 and mem_cgroup_flush_stats_ratelimited() reading it directly.

Unlike jiffies, jiffies_64 is not volatile, so raw reads are plain
accesses and can even be torn on 32-bit.  Use get_jiffies_64() instead,
and fix the same pattern in mem_cgroup_flush_foreign().

Link: https://lore.kernel.org/20260827025457.116191-1-jiayuan.chen@linux.dev
Fixes: 508bed884767 ("mm: memcg: change flush_next_time to flush_last_time")
Fixes: 97b27821b485 ("writeback, memcg: Implement foreign dirty flushing")
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: syzbot+ced4d9a8cadb5ef3adae@syzkaller.appspotmail.com
Acked-by: Muchun Song <muchun.song@linux.dev>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: <stable@vger.kernel.org>
---
 mm/memcontrol.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 856a7d07586cc..d399710e9799a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -757,7 +757,7 @@ static void __mem_cgroup_flush_stats(struct mem_cgroup *memcg, bool force)
 		return;
 
 	if (mem_cgroup_is_root(memcg))
-		WRITE_ONCE(flush_last_time, jiffies_64);
+		WRITE_ONCE(flush_last_time, get_jiffies_64());
 
 	css_rstat_flush(&memcg->css);
 }
@@ -785,7 +785,7 @@ void mem_cgroup_flush_stats(struct mem_cgroup *memcg)
 void mem_cgroup_flush_stats_ratelimited(struct mem_cgroup *memcg)
 {
 	/* Only flush if the periodic flusher is one full cycle late */
-	if (time_after64(jiffies_64, READ_ONCE(flush_last_time) + 2*FLUSH_TIME))
+	if (time_after64(get_jiffies_64(), READ_ONCE(flush_last_time) + 2 * FLUSH_TIME))
 		mem_cgroup_flush_stats(memcg);
 }
 
@@ -3946,7 +3946,7 @@ void mem_cgroup_flush_foreign(struct bdi_writeback *wb)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_css(wb->memcg_css);
 	unsigned long intv = msecs_to_jiffies(dirty_expire_interval * 10);
-	u64 now = jiffies_64;
+	u64 now = get_jiffies_64();
 	int i;
 
 	for (i = 0; i < MEMCG_CGWB_FRN_CNT; i++) {
-- 
2.53.0