On 2020/01/29 21:03, Michal Hocko wrote:
>> Fixes: 3e32cb2e0a12 ("mm: memcontrol: lockless page counters")
>> Signed-off-by: Qian Cai <cai@xxxxxx>
>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Please include
Reported-by: syzbot+f36cfe60b1006a94f9dc@xxxxxxxxxxxxxxxxxxxxxxxxx
for https://syzkaller.appspot.com/bug?id=744097b8b91cecd8b035a6f746bb12e4efc7669f .
By the way, can READ_ONCE()/WRITE_ONCE() really solve this warning?
The link above says read/write on the same location ( mm/page_counter.c:129 ).
I don't know how READ_ONCE()/WRITE_ONCE() can solve the race.
>
>> ---
>> mm/page_counter.c | 8 ++++----
>> 1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/page_counter.c b/mm/page_counter.c
>> index de31470655f6..a17841150906 100644
>> --- a/mm/page_counter.c
>> +++ b/mm/page_counter.c
>> @@ -82,8 +82,8 @@ void page_counter_charge(struct page_counter *counter, unsigned long nr_pages)
>> * This is indeed racy, but we can live with some
>> * inaccuracy in the watermark.
>> */
>> - if (new > c->watermark)
>> - c->watermark = new;
>> + if (new > READ_ONCE(c->watermark))
>> + WRITE_ONCE(c->watermark, new);
>> }
>> }
>>
>> @@ -135,8 +135,8 @@ bool page_counter_try_charge(struct page_counter *counter,
>> * Just like with failcnt, we can live with some
>> * inaccuracy in the watermark.
>> */
>> - if (new > c->watermark)
>> - c->watermark = new;
>> + if (new > READ_ONCE(c->watermark))
>> + WRITE_ONCE(c->watermark, new);
>> }
>> return true;
>>
>> --
>> 2.21.0 (Apple Git-122.2)
>
