Re: [RFC][PATCH 1/4] memcg: fix formem_cgroup_get_reclaim_stat_from_page

[KAMEZAWA Hiroyuki]

Daisuke Nishimura said:

>     Call Trace:
>      [<ffffffff8028ea17>] ? ____pagevec_lru_add+0xc1/0x13c
>      [<ffffffff8028ec34>] ? drain_cpu_pagevecs+0x36/0x89
>      [<ffffffff802a4f8c>] ? swapin_readahead+0x78/0x98
>      [<ffffffff8029a37a>] ? handle_mm_fault+0x3d9/0x741
>      [<ffffffff804da654>] ? do_page_fault+0x3ce/0x78c
>      [<ffffffff804d7a42>] ? trace_hardirqs_off_thunk+0x3a/0x3c
>      [<ffffffff804d860f>] ? page_fault+0x1f/0x30
>     Code: cc 55 48 8d af b8 0d 00 00 48 89 f7 53 89 d3 e8 39 85 02 00 48
> 63 d3 48 ff 44 d5 10 45 85 e4 74 05 48 ff 44 d5 00 48 85 c0 74 0e <48>
> ff 44 d0 10 45 85 e4 74 04 48 ff 04 d0 5b 5d 41 5c c3 41 54
>     RIP  [<ffffffff8028e710>] update_page_reclaim_stat+0x2f/0x42
>      RSP <ffff8801ee457da8>
>
>
> Signed-off-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
yes. PageCgroupUsed() should be cheked.
or
list_empty(&pc->lru) should be checked under zone->lock.
Your fix seems reasonable.

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

> ---
>  mm/memcontrol.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e2996b8..62e69d8 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -559,6 +559,10 @@ mem_cgroup_get_reclaim_stat_from_page(struct page
> *page)
>  		return NULL;
>
>  	pc = lookup_page_cgroup(page);
> +	smp_rmb();
> +	if (!PageCgroupUsed(pc))
> +		return NULL;
> +
>  	mz = page_cgroup_zoneinfo(pc);
>  	if (!mz)
>  		return NULL;
> --
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