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Date: Tue, 6 Jun 2017 21:39:36 +0800
From: zhong jiang <zhongjiang@huawei.com>
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To: Michal Hocko <mhocko@kernel.org>, Vlastimil Babka <vbabka@suse.cz>,
        "David Rientjes" <rientjes@google.com>,
        Hugh Dickins <hughd@google.com>, "Oleg Nesterov" <oleg@redhat.com>
CC: Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>, Xishi Qiu <qiuxishi@huawei.com>
Subject: double call identical release when there is a race hitting
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Hi

when I review the code, I find the following scenario will lead to a race ,
but I am not sure whether the real issue will hit or not.

cpu1                                                                      cpu2
exit_mmap                                               mmu_notifier_unregister
   __mmu_notifier_release                                 srcu_read_lock
            srcu_read_lock
            mm->ops->release(mn, mm)                 mm->ops->release(mn,mm)
           srcu_read_unlock                                         srcu_read_unlock


obviously,  the specified mm will call identical release function when
the related condition satisfy.  is it right?

Thanks
zhongjiang