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    SubjectRe: [BUGFIX][PATCH -stable] memcg: avoid oom-killing innocent task in case of use_hierarchy
    * nishimura@mxp.nes.nec.co.jp <nishimura@mxp.nes.nec.co.jp> [2009-11-24 16:28:54]:

    > task_in_mem_cgroup(), which is called by select_bad_process() to check whether
    > a task can be a candidate for being oom-killed from memcg's limit, checks
    > "curr->use_hierarchy"("curr" is the mem_cgroup the task belongs to).
    >
    > But this check return true(it's false positive) when:
    >
    > <some path>/00 use_hierarchy == 0 <- hitting limit
    > <some path>/00/aa use_hierarchy == 1 <- "curr"
    >
    > This leads to killing an innocent task in 00/aa. This patch is a fix for this
    > bug. And this patch also fixes the arg for mem_cgroup_print_oom_info(). We
    > should print information of mem_cgroup which the task being killed, not current,
    > belongs to.
    >
    > Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
    > ---
    > mm/memcontrol.c | 2 +-
    > mm/oom_kill.c | 2 +-
    > 2 files changed, 2 insertions(+), 2 deletions(-)
    >
    > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    > index fd4529d..3acc226 100644
    > --- a/mm/memcontrol.c
    > +++ b/mm/memcontrol.c
    > @@ -496,7 +496,7 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
    > task_unlock(task);
    > if (!curr)
    > return 0;
    > - if (curr->use_hierarchy)
    > + if (mem->use_hierarchy)
    > ret = css_is_ancestor(&curr->css, &mem->css);
    > else
    > ret = (curr == mem);
    > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
    > index a7b2460..ed452e9 100644
    > --- a/mm/oom_kill.c
    > +++ b/mm/oom_kill.c
    > @@ -400,7 +400,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
    > cpuset_print_task_mems_allowed(current);
    > task_unlock(current);
    > dump_stack();
    > - mem_cgroup_print_oom_info(mem, current);
    > + mem_cgroup_print_oom_info(mem, p);
    > show_mem();
    > if (sysctl_oom_dump_tasks)
    > dump_tasks(mem);
    >


    Reviewed-by: Balbir Singh <balbir@linux.vnet.ibm.com>


    --
    Balbir


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