linux-kernel - Re: [RFC PATCH] mm: thp: grab the lock before manipulation defer list

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Message-ID: <20200107012241.GA15341@richard>
Date:   Tue, 7 Jan 2020 09:22:41 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Wei Yang <richardw.yang@...ux.intel.com>, hannes@...xchg.org,
        vdavydov.dev@...il.com, akpm@...ux-foundation.org,
        kirill.shutemov@...ux.intel.com, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        yang.shi@...ux.alibaba.com
Subject: Re: [RFC PATCH] mm: thp: grab the lock before manipulation defer list

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