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

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Date:   Fri, 3 Jan 2020 16:44:59 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Wei Yang <richardw.yang@...ux.intel.com>
cc:     hannes@...xchg.org, mhocko@...nel.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 Sat, 4 Jan 2020, Wei Yang wrote:

> On Fri, Jan 03, 2020 at 11:29:06AM -0800, David Rientjes wrote:
> >On Fri, 3 Jan 2020, Wei Yang wrote:
> >
> >> As all the other places, we grab the lock before manipulate the defer list.
> >> Current implementation may face a race condition.
> >> 
> >> Fixes: 87eaceb3faa5 ("mm: thp: make deferred split shrinker memcg aware")
> >> 
> >> Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
> >> 
> >> ---
> >> I notice the difference during code reading and just confused about the
> >> difference. No specific test is done since limited knowledge about cgroup.
> >> 
> >> Maybe I miss something important?
> >
> >The check for !list_empty(page_deferred_list(page)) must certainly be 
> >serialized with doing list_del_init(page_deferred_list(page)).
> >
> 
> Hi David
> 
> Would you mind giving more information? You mean list_empty and list_del_init
> is atomic?
> 

I mean your patch is obviously correct :)  It should likely also have a 
stable@...r.kernel.org # 5.4+

Acked-by: David Rientjes <rientjes@...gle.com>