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mm/memcontrol: fix data-race on reading jiffies_64

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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: 508bed8847 ("mm: memcg: change flush_next_time to flush_last_time")
Fixes: 97b27821b4 ("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>
This commit is contained in:
Jiayuan Chen 2026-08-27 10:54:56 +08:00 committed by Andrew Morton
parent 576446e2df
commit c20cf1c3c8
1 changed files with 3 additions and 3 deletions
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6
mm/memcontrol.c
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@ -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++) {