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    Subject[PATCH 3.13 013/120] mm/memcg: iteration skip memcgs not yet fully initialized
    Date
    3.13-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Hugh Dickins <hughd@google.com>

    commit d8ad30559715ce97afb7d1a93a12fd90e8fff312 upstream.

    It is surprising that the mem_cgroup iterator can return memcgs which
    have not yet been fully initialized. By accident (or trial and error?)
    this appears not to present an actual problem; but it may be better to
    prevent such surprises, by skipping memcgs not yet online.

    Signed-off-by: Hugh Dickins <hughd@google.com>
    Cc: Tejun Heo <tj@kernel.org>
    Acked-by: Michal Hocko <mhocko@suse.cz>
    Cc: Johannes Weiner <hannes@cmpxchg.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>

    ---
    mm/memcontrol.c | 6 ++----
    1 file changed, 2 insertions(+), 4 deletions(-)

    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -1100,10 +1100,8 @@ skip_node:
    * protected by css_get and the tree walk is rcu safe.
    */
    if (next_css) {
    - struct mem_cgroup *mem = mem_cgroup_from_css(next_css);
    -
    - if (css_tryget(&mem->css))
    - return mem;
    + if ((next_css->flags & CSS_ONLINE) && css_tryget(next_css))
    + return mem_cgroup_from_css(next_css);
    else {
    prev_css = next_css;
    goto skip_node;



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