• Johannes Weiner's avatar
    mm: memcontrol: do not iterate uninitialized memcgs · 2f7dd7a4
    Johannes Weiner authored
    The cgroup iterators yield css objects that have not yet gone through
    css_online(), but they are not complete memcgs at this point and so the
    memcg iterators should not return them.  Commit d8ad3055
    iteration skip memcgs not yet fully initialized") set out to implement
    exactly this, but it uses CSS_ONLINE, a cgroup-internal flag that does
    not meet the ordering requirements for memcg, and so the iterator may
    skip over initialized groups, or return partially initialized memcgs.
    The cgroup core can not reasonably provide a clear answer on whether the
    object around the css has been fully initialized, as that depends on
    controller-specific locking and lifetime rules.  Thus, introduce a
    memcg-specific flag that is set after the memcg has been initialized in
    css_online(), and read before mem_cgroup_iter() callers access the memcg
    Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
    Cc: Tejun Heo <tj@kernel.org>
    Acked-by: default avatarMichal Hocko <mhocko@suse.cz>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: <stable@vger.kernel.org>	[3.12+]
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>