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    SubjectRe: [BUGFIX][PATCH] memcg rcu lock fix v3
    > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    >
    > css_id() should be called under rcu_read_lock().
    > Following is a report from Li Zefan.
    > ==
    > ===================================================
    > [ INFO: suspicious rcu_dereference_check() usage. ]
    > ---------------------------------------------------
    > kernel/cgroup.c:4438 invoked rcu_dereference_check() without protection!
    >
    > other info that might help us debug this:
    >
    >
    > rcu_scheduler_active = 1, debug_locks = 1
    > 1 lock held by kswapd0/31:
    > #0: (swap_lock){+.+.-.}, at: [<c05058bb>] swap_info_get+0x4b/0xd0
    >
    > stack backtrace:
    ...
    >
    > And css_is_ancestor() should be called under rcu_read_lock().
    >
    >
    > Reported-by: Li Zefan <lizf@cn.fujitsu.com>
    > Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
    > Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
    > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

    With this patch applied, I did some more test, and no warning was triggered.

    Tested-by: Li Zefan <lizf@cn.fujitsu.com>



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