linux-kernel - Re: [PATCH v20 17/20] mm/swap.c: serialize memcg changes in pagevec_lru_move

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Date:   Mon, 2 Nov 2020 10:20:45 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Alex Shi <alex.shi@...ux.alibaba.com>
Cc:     akpm@...ux-foundation.org, mgorman@...hsingularity.net,
        tj@...nel.org, hughd@...gle.com, khlebnikov@...dex-team.ru,
        daniel.m.jordan@...cle.com, willy@...radead.org, lkp@...el.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, shakeelb@...gle.com,
        iamjoonsoo.kim@....com, richard.weiyang@...il.com,
        kirill@...temov.name, alexander.duyck@...il.com,
        rong.a.chen@...el.com, mhocko@...e.com, vdavydov.dev@...il.com,
        shy828301@...il.com
Subject: Re: [PATCH v20 17/20] mm/swap.c: serialize memcg changes in
 pagevec_lru_move_fn

On Thu, Oct 29, 2020 at 06:45:02PM +0800, Alex Shi wrote:
> Hugh Dickins' found a memcg change bug on original version:
> If we want to change the pgdat->lru_lock to memcg's lruvec lock, we have
> to serialize mem_cgroup_move_account during pagevec_lru_move_fn. The
> possible bad scenario would like:
> 
> 	cpu 0					cpu 1
> lruvec = mem_cgroup_page_lruvec()
> 					if (!isolate_lru_page())
> 						mem_cgroup_move_account
> 
> spin_lock_irqsave(&lruvec->lru_lock <== wrong lock.
> 
> So we need TestClearPageLRU to block isolate_lru_page(), that serializes
> the memcg change. and then removing the PageLRU check in move_fn callee
> as the consequence.
> 
> __pagevec_lru_add_fn() is different from the others, because the pages
> it deals with are, by definition, not yet on the lru.  TestClearPageLRU
> is not needed and would not work, so __pagevec_lru_add() goes its own
> way.
> 
> Reported-by: Hugh Dickins <hughd@...gle.com>
> Signed-off-by: Alex Shi <alex.shi@...ux.alibaba.com>
> Acked-by: Hugh Dickins <hughd@...gle.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org

Acked-by: Johannes Weiner <hannes@...xchg.org>