mm/percpu: prevent concurrency problem for pcpu_nr_populated read with spin lock

mm/percpu: prevent concurrency problem for pcpu_nr_populated read with spin lock

pcpu_nr_pages() reads pcpu_nr_populated without any protection, which
causes a data race between read/write.

However, since this is an intended race, we should add a data_race
annotation instead of add a spin lock.

[akpm@linux-foundation.org: move pcpu_nr_units multiplication outside data_race(), per Vlastimil]
Link: https://lkml.kernel.org/r/20250703065600.132221-1-aha310510@gmail.com
Fixes: 7e8a6304d541 ("/proc/meminfo: add percpu populated pages count")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
Reported-by: syzbot+e5bd32b79413e86f389e@syzkaller.appspotmail.com
Suggested-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Christoph Lameter (Ampere) <cl@gentwo.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>