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    Subject[PATCH 4.19 40/73] memcg: make it work on sparse non-0-node systems
    Date
    From: Jiri Slaby <jslaby@suse.cz>

    commit 3e8589963773a5c23e2f1fe4bcad0e9a90b7f471 upstream.

    We have a single node system with node 0 disabled:
    Scanning NUMA topology in Northbridge 24
    Number of physical nodes 2
    Skipping disabled node 0
    Node 1 MemBase 0000000000000000 Limit 00000000fbff0000
    NODE_DATA(1) allocated [mem 0xfbfda000-0xfbfeffff]

    This causes crashes in memcg when system boots:
    BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
    #PF error: [normal kernel read fault]
    ...
    RIP: 0010:list_lru_add+0x94/0x170
    ...
    Call Trace:
    d_lru_add+0x44/0x50
    dput.part.34+0xfc/0x110
    __fput+0x108/0x230
    task_work_run+0x9f/0xc0
    exit_to_usermode_loop+0xf5/0x100

    It is reproducible as far as 4.12. I did not try older kernels. You have
    to have a new enough systemd, e.g. 241 (the reason is unknown -- was not
    investigated). Cannot be reproduced with systemd 234.

    The system crashes because the size of lru array is never updated in
    memcg_update_all_list_lrus and the reads are past the zero-sized array,
    causing dereferences of random memory.

    The root cause are list_lru_memcg_aware checks in the list_lru code. The
    test in list_lru_memcg_aware is broken: it assumes node 0 is always
    present, but it is not true on some systems as can be seen above.

    So fix this by avoiding checks on node 0. Remember the memcg-awareness by
    a bool flag in struct list_lru.

    Link: http://lkml.kernel.org/r/20190522091940.3615-1-jslaby@suse.cz
    Fixes: 60d3fd32a7a9 ("list_lru: introduce per-memcg lists")
    Signed-off-by: Jiri Slaby <jslaby@suse.cz>
    Acked-by: Michal Hocko <mhocko@suse.com>
    Suggested-by: Vladimir Davydov <vdavydov.dev@gmail.com>
    Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
    Reviewed-by: Shakeel Butt <shakeelb@google.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    include/linux/list_lru.h | 1 +
    mm/list_lru.c | 8 +++-----
    2 files changed, 4 insertions(+), 5 deletions(-)

    --- a/include/linux/list_lru.h
    +++ b/include/linux/list_lru.h
    @@ -54,6 +54,7 @@ struct list_lru {
    #ifdef CONFIG_MEMCG_KMEM
    struct list_head list;
    int shrinker_id;
    + bool memcg_aware;
    #endif
    };

    --- a/mm/list_lru.c
    +++ b/mm/list_lru.c
    @@ -37,11 +37,7 @@ static int lru_shrinker_id(struct list_l

    static inline bool list_lru_memcg_aware(struct list_lru *lru)
    {
    - /*
    - * This needs node 0 to be always present, even
    - * in the systems supporting sparse numa ids.
    - */
    - return !!lru->node[0].memcg_lrus;
    + return lru->memcg_aware;
    }

    static inline struct list_lru_one *
    @@ -451,6 +447,8 @@ static int memcg_init_list_lru(struct li
    {
    int i;

    + lru->memcg_aware = memcg_aware;
    +
    if (!memcg_aware)
    return 0;


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