> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
quoted text
> 
> 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:
...
quoted text
> 
> 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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