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SubjectRe: [PATCH] mm/vmstat: annotate data race for zone->free_area[order].nr_free
On Wed, 8 Sep 2021 09:56:06 +0800 Liu Shixin <liushixin2@huawei.com> wrote:

> KCSAN reports a data-race on v5.10 which also exists on mainline:
>
> ==================================================================
> BUG: KCSAN: data-race in extfrag_for_order+0x33/0x2d0
>
> race at unknown origin, with read to 0xffff9ee9bfffab48 of 8 bytes by task 34 on cpu 1:
> extfrag_for_order+0x33/0x2d0
> kcompactd+0x5f0/0xce0
> kthread+0x1f9/0x220
> ret_from_fork+0x22/0x30
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 PID: 34 Comm: kcompactd0 Not tainted 5.10.0+ #2
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
> ==================================================================
>
> Access to zone->free_area[order].nr_free in extfrag_for_order()/frag_show_print()
> is lockless. That's intentional and the stats are a rough estimate anyway.
> Annotate them with data_race().

checkpatch helpfully says

WARNING: data_race without comment
#40: FILE: mm/vmstat.c:1074:
+ blocks = data_race(zone->free_area[order].nr_free);


can we please add a comment ;)

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