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    SubjectRe: [RFC][PATCH -mmotm 3/4] memcg: avoid dead lock caused by racebetween oom and cpuset_attach
    From
    Daisuke Nishimura said:
    > mpol_rebind_mm(), which can be called from cpuset_attach(), does
    > down_write(mm->mmap_sem).
    > This means down_write(mm->mmap_sem) can be called under cgroup_mutex.
    >
    > OTOH, page fault path does down_read(mm->mmap_sem) and calls
    > mem_cgroup_try_charge_xxx(),
    > which may eventually calls mem_cgroup_out_of_memory(). And
    > mem_cgroup_out_of_memory()
    > calls cgroup_lock().
    > This means cgroup_lock() can be called under down_read(mm->mmap_sem).
    >
    good catch.

    > If those two paths race, dead lock can happen.
    >
    > This patch avoid this dead lock by:
    > - remove cgroup_lock() from mem_cgroup_out_of_memory().
    agree to this.

    > - define new mutex (memcg_tasklist) and serialize mem_cgroup_move_task()
    > (->attach handler of memory cgroup) and mem_cgroup_out_of_memory.
    >
    Hmm...seems temporal fix (and adding new global lock...)
    But ok, we need fix. revist this later.

    Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu,com>




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