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    SubjectRe: [PATCH] memcg: fix Bad page state after replace_page_cache
    On Wed, Apr 18, 2012 at 11:34:46PM -0700, Hugh Dickins wrote:
    > My 9ce70c0240d0 "memcg: fix deadlock by inverting lrucare nesting" put a
    > nasty little bug into v3.3's version of mem_cgroup_replace_page_cache(),
    > sometimes used for FUSE. Replacing __mem_cgroup_commit_charge_lrucare()
    > by __mem_cgroup_commit_charge(), I used the "pc" pointer set up earlier:
    > but it's for oldpage, and needs now to be for newpage. Once oldpage was
    > freed, its PageCgroupUsed bit (cleared above but set again here) caused
    > "Bad page state" messages - and perhaps worse, being missed from newpage.
    > (I didn't find this by using FUSE, but in reusing the function for tmpfs.)
    > Signed-off-by: Hugh Dickins <>
    > Cc: [v3.3 only]

    Acked-by: Johannes Weiner <>

    This is the second bug of this nature and none of the callsites are
    actually using the pc themselves, so we should probably move the pc
    lookup into __mem_cgroup_commit_charge() itself.

    From: Johannes Weiner <>
    Subject: [patch] mm: memcg: move pc lookup point to commit_charge()

    None of the callsites actually need the page_cgroup descriptor
    themselves, so just pass the page and do the look up in there.

    We already had two bugs (6568d4a 'mm: memcg: update the correct soft
    limit tree during migration' and 'memcg: fix Bad page state after
    replace_page_cache') where the passed page and pc were not referring
    to the same page frame.

    Signed-off-by: Johannes Weiner <>
    mm/memcontrol.c | 17 +++++------------
    1 files changed, 5 insertions(+), 12 deletions(-)

    diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    index 884e936..1a28dd8 100644
    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -2461,10 +2461,10 @@ struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
    static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
    struct page *page,
    unsigned int nr_pages,
    - struct page_cgroup *pc,
    enum charge_type ctype,
    bool lrucare)
    + struct page_cgroup *pc = lookup_page_cgroup(page);
    struct zone *uninitialized_var(zone);
    bool was_on_lru = false;
    bool anon;
    @@ -2701,7 +2701,6 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
    struct mem_cgroup *memcg = NULL;
    unsigned int nr_pages = 1;
    - struct page_cgroup *pc;
    bool oom = true;
    int ret;

    @@ -2715,11 +2714,10 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
    oom = false;

    - pc = lookup_page_cgroup(page);
    ret = __mem_cgroup_try_charge(mm, gfp_mask, nr_pages, &memcg, oom);
    if (ret == -ENOMEM)
    return ret;
    - __mem_cgroup_commit_charge(memcg, page, nr_pages, pc, ctype, false);
    + __mem_cgroup_commit_charge(memcg, page, nr_pages, ctype, false);
    return 0;

    @@ -2816,16 +2814,13 @@ static void
    __mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *memcg,
    enum charge_type ctype)
    - struct page_cgroup *pc;
    if (mem_cgroup_disabled())
    if (!memcg)

    - pc = lookup_page_cgroup(page);
    - __mem_cgroup_commit_charge(memcg, page, 1, pc, ctype, true);
    + __mem_cgroup_commit_charge(memcg, page, 1, ctype, true);
    * Now swap is on-memory. This means this page may be
    * counted both as mem and swap....double count.
    @@ -3254,14 +3249,13 @@ int mem_cgroup_prepare_migration(struct page *page,
    * page. In the case new page is migrated but not remapped, new page's
    * mapcount will be finally 0 and we call uncharge in end_migration().
    - pc = lookup_page_cgroup(newpage);
    if (PageAnon(page))
    else if (page_is_file_cache(page))
    - __mem_cgroup_commit_charge(memcg, newpage, 1, pc, ctype, false);
    + __mem_cgroup_commit_charge(memcg, newpage, 1, ctype, false);
    return ret;

    @@ -3348,8 +3342,7 @@ void mem_cgroup_replace_page_cache(struct page *oldpage,
    * the newpage may be on LRU(or pagevec for LRU) already. We lock
    * LRU while we overwrite pc->mem_cgroup.
    - pc = lookup_page_cgroup(newpage);
    - __mem_cgroup_commit_charge(memcg, newpage, 1, pc, type, true);
    + __mem_cgroup_commit_charge(memcg, newpage, 1, type, true);

    #ifdef CONFIG_DEBUG_VM

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