+ mm-memcontrol-fix-data-race-on-reading-jiffies_64.patch added to mm-new branch

+ mm-memcontrol-fix-data-race-on-reading-jiffies_64.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/memcontrol: fix data-race on reading jiffies_64
has been added to the -mm mm-new branch.  Its filename is
     mm-memcontrol-fix-data-race-on-reading-jiffies_64.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memcontrol-fix-data-race-on-reading-jiffies_64.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Jiayuan Chen <jiayuan.chen@linux.dev>
Subject: mm/memcontrol: fix data-race on reading jiffies_64
Date: Thu, 27 Aug 2026 10:54:56 +0800

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>
Reported-by: syzbot+ced4d9a8cadb5ef3adae@syzkaller.appspotmail.com
Acked-by: Muchun Song <muchun.song@linux.dev>
Cc: Chris Li <chrisl@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memcontrol.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/mm/memcontrol.c~mm-memcontrol-fix-data-race-on-reading-jiffies_64
+++ a/mm/memcontrol.c
@@ -757,7 +757,7 @@ static void __mem_cgroup_flush_stats(str
 		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_c
 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);
 }
 
@@ -3945,7 +3945,7 @@ void mem_cgroup_flush_foreign(struct bdi
 {
 	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++) {
_

Patches currently in -mm which might be from jiayuan.chen@linux.dev are

mm-memcontrol-fix-data-race-on-reading-jiffies_64.patch