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    SubjectRe: [RFC][PATCH 1/4] memcg: fix formem_cgroup_get_reclaim_stat_from_page
    From
    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@mxp.nes.nec.co.jp>
    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@jp.fujitsu.com>

    > ---
    > 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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