+ mm-percpu-prevent-concurrency-problem-for-pcpu_nr_populated-read-with-spin-lock.patch added to mm-unstable branch

+ mm-percpu-prevent-concurrency-problem-for-pcpu_nr_populated-read-with-spin-lock.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/percpu: prevent concurrency problem for pcpu_nr_populated read with spin lock
has been added to the -mm mm-unstable branch.  Its filename is
     mm-percpu-prevent-concurrency-problem-for-pcpu_nr_populated-read-with-spin-lock.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-percpu-prevent-concurrency-problem-for-pcpu_nr_populated-read-with-spin-lock.patch

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

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------------------------------------------------------
From: Jeongjun Park <aha310510@gmail.com>
Subject: mm/percpu: prevent concurrency problem for pcpu_nr_populated read with spin lock
Date: Thu, 3 Jul 2025 15:56:00 +0900

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.

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>
---

 mm/percpu.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/percpu.c~mm-percpu-prevent-concurrency-problem-for-pcpu_nr_populated-read-with-spin-lock
+++ a/mm/percpu.c
@@ -3355,7 +3355,7 @@ void __init setup_per_cpu_areas(void)
  */
 unsigned long pcpu_nr_pages(void)
 {
-	return pcpu_nr_populated * pcpu_nr_units;
+	return data_race(READ_ONCE(pcpu_nr_populated) * pcpu_nr_units);
 }
 
 /*
_

Patches currently in -mm which might be from aha310510@gmail.com are

mm-maps-execute-procmap_query-ioctl-under-per-vma-locks-fix.patch
mm-percpu-prevent-concurrency-problem-for-pcpu_nr_populated-read-with-spin-lock.patch