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Date:   Tue, 7 Jan 2020 09:22:41 +0800
From:   Wei Yang <richardw.yang@linux.intel.com>
To:     Michal Hocko <mhocko@kernel.org>
Cc:     Wei Yang <richardw.yang@linux.intel.com>, hannes@cmpxchg.org,
        vdavydov.dev@gmail.com, akpm@linux-foundation.org,
        kirill.shutemov@linux.intel.com, cgroups@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        yang.shi@linux.alibaba.com
Subject: Re: [RFC PATCH] mm: thp: grab the lock before manipulation defer list
Message-ID: <20200107012241.GA15341@richard>
Reply-To: Wei Yang <richardw.yang@linux.intel.com>
References: <20200103143407.1089-1-richardw.yang@linux.intel.com>
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On Mon, Jan 06, 2020 at 11:23:45AM +0100, Michal Hocko wrote:
>On Fri 03-01-20 22:34:07, Wei Yang wrote:
>> As all the other places, we grab the lock before manipulate the defer list.
>> Current implementation may face a race condition.
>
>Please always make sure to describe the effect of the change. Why a racy
>list_empty check matters?
>

Hmm... access the list without proper lock leads to many bad behaviors.

For example, if we grab the lock after checking list_empty, the page may
already be removed from list in split_huge_page_list. And then list_del_init
would trigger bug.

-- 
Wei Yang
Help you, Help me