• Hugh Dickins's avatar
    memcg: fix hotplugged memory zone oops · bea8c150
    Hugh Dickins authored
    When MEMCG is configured on (even when it's disabled by boot option),
    when adding or removing a page to/from its lru list, the zone pointer
    used for stats updates is nowadays taken from the struct lruvec.  (On
    many configurations, calculating zone from page is slower.)
    
    But we have no code to update all the lruvecs (per zone, per memcg) when
    a memory node is hotadded.  Here's an extract from the oops which
    results when running numactl to bind a program to a newly onlined node:
    
      BUG: unable to handle kernel NULL pointer dereference at 0000000000000f60
      IP:  __mod_zone_page_state+0x9/0x60
      Pid: 1219, comm: numactl Not tainted 3.6.0-rc5+ #180 Bochs Bochs
      Process numactl (pid: 1219, threadinfo ffff880039abc000, task ffff8800383c4ce0)
      Call Trace:
        __pagevec_lru_add_fn+0xdf/0x140
        pagevec_lru_move_fn+0xb1/0x100
        __pagevec_lru_add+0x1c/0x30
        lru_add_drain_cpu+0xa3/0x130
        lru_add_drain+0x2f/0x40
       ...
    
    The natural solution might be to use a memcg callback whenever memory is
    hotadded; but that solution has not been scoped out, and it happens that
    we do have an easy location at which to update lruvec->zone.  The lruvec
    pointer is discovered either by mem_cgroup_zone_lruvec() or by
    mem_cgroup_page_lruvec(), and both of those do know the right zone.
    
    So check and set lruvec->zone in those; and remove the inadequate
    attempt to set lruvec->zone from lruvec_init(), which is called before
    NODE_DATA(node) has been allocated in such cases.
    
    Ah, there was one exceptionr.  For no particularly good reason,
    mem_cgroup_force_empty_list() has its own code for deciding lruvec.
    Change it to use the standard mem_cgroup_zone_lruvec() and
    mem_cgroup_get_lru_size() too.  In fact it was already safe against such
    an oops (the lru lists in danger could only be empty), but we're better
    proofed against future changes this way.
    
    I've marked this for stable (3.6) since we introduced the problem in 3.5
    (now closed to stable); but I have no idea if this is the only fix
    needed to get memory hotadd working with memcg in 3.6, and received no
    answer when I enquired twice before.
    Reported-by: default avatarTang Chen <tangchen@cn.fujitsu.com>
    Signed-off-by: default avatarHugh Dickins <hughd@google.com>
    Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
    Acked-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
    Cc: Wen Congyang <wency@cn.fujitsu.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    bea8c150
mmzone.c 1.9 KB