From: Hugh Dickins <hughd@google.com>
To: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
mgorman@techsingularity.net, tj@kernel.org, hughd@google.com,
khlebnikov@yandex-team.ru, daniel.m.jordan@oracle.com,
willy@infradead.org, hannes@cmpxchg.org, lkp@intel.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
cgroups@vger.kernel.org, shakeelb@google.com,
iamjoonsoo.kim@lge.com, richard.weiyang@gmail.com,
kirill@shutemov.name, alexander.duyck@gmail.com,
rong.a.chen@intel.com, mhocko@suse.com, vdavydov.dev@gmail.com,
shy828301@gmail.com, Minchan Kim <minchan@kernel.org>
Subject: Re: [PATCH v21 06/19] mm/rmap: stop store reordering issue on page->mapping
Date: Tue, 10 Nov 2020 23:41:52 -0800 (PST) [thread overview]
Message-ID: <alpine.LSU.2.11.2011102330040.1183@eggly.anvils> (raw)
In-Reply-To: <e66ef2e5-c74c-6498-e8b3-56c37b9d2d15@linux.alibaba.com>
On Fri, 6 Nov 2020, Alex Shi wrote:
>
> updated for comments change from Johannes
>
>
> From 2fd278b1ca6c3e260ad249808b62f671d8db5a7b Mon Sep 17 00:00:00 2001
> From: Alex Shi <alex.shi@linux.alibaba.com>
> Date: Thu, 5 Nov 2020 11:38:24 +0800
> Subject: [PATCH v21 06/19] mm/rmap: stop store reordering issue on
> page->mapping
>
> Hugh Dickins and Minchan Kim observed a long time issue which
> discussed here, but actully the mentioned fix missed.
> https://lore.kernel.org/lkml/20150504031722.GA2768@blaptop/
> The store reordering may cause problem in the scenario:
>
> CPU 0 CPU1
> do_anonymous_page
> page_add_new_anon_rmap()
> page->mapping = anon_vma + PAGE_MAPPING_ANON
> lru_cache_add_inactive_or_unevictable()
> spin_lock(lruvec->lock)
> SetPageLRU()
> spin_unlock(lruvec->lock)
> /* idletacking judged it as LRU
> * page so pass the page in
> * page_idle_clear_pte_refs
> */
> page_idle_clear_pte_refs
> rmap_walk
> if PageAnon(page)
>
> Johannes give detailed examples how the store reordering could cause
> a trouble:
> "The concern is the SetPageLRU may get reorder before 'page->mapping'
> setting, That would make CPU 1 will observe at page->mapping after
> observing PageLRU set on the page.
>
> 1. anon_vma + PAGE_MAPPING_ANON
>
> That's the in-order scenario and is fine.
>
> 2. NULL
>
> That's possible if the page->mapping store gets reordered to occur
> after SetPageLRU. That's fine too because we check for it.
>
> 3. anon_vma without the PAGE_MAPPING_ANON bit
>
> That would be a problem and could lead to all kinds of undesirable
> behavior including crashes and data corruption.
>
> Is it possible? AFAICT the compiler is allowed to tear the store to
> page->mapping and I don't see anything that would prevent it.
>
> That said, I also don't see how the reader testing PageLRU under the
> lru_lock would prevent that in the first place. AFAICT we need that
> WRITE_ONCE() around the page->mapping assignment."
>
> Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Hugh Dickins <hughd@google.com>
Acked-by: Hugh Dickins <hughd@google.com>
Many thanks to Johannes for spotting my falsehood in the next patch,
and to Alex for making it true with this patch. As I just remarked
against the v20, I do have some more of these WRITE_ONCEs, but consider
them merely theoretical: so please don't let me hold this series up.
Andrew, I am hoping that Alex's v21 will appear in the next mmotm?
Thanks,
Hugh
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-mm@kvack.org
> ---
> mm/rmap.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 1b84945d655c..380c6b9956c2 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1054,8 +1054,14 @@ static void __page_set_anon_rmap(struct page *page,
> if (!exclusive)
> anon_vma = anon_vma->root;
>
> + /*
> + * page_idle does a lockless/optimistic rmap scan on page->mapping.
> + * Make sure the compiler doesn't split the stores of anon_vma and
> + * the PAGE_MAPPING_ANON type identifier, otherwise the rmap code
> + * could mistake the mapping for a struct address_space and crash.
> + */
> anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
> - page->mapping = (struct address_space *) anon_vma;
> + WRITE_ONCE(page->mapping, (struct address_space *) anon_vma);
> page->index = linear_page_index(vma, address);
> }
>
> --
> 1.8.3.1
next prev parent reply other threads:[~2020-11-11 7:41 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-05 8:55 [PATCH v21 00/19] per memcg lru lock Alex Shi
2020-11-05 8:55 ` [PATCH v21 01/19] mm/thp: move lru_add_page_tail func to huge_memory.c Alex Shi
2020-11-05 8:55 ` [PATCH v21 02/19] mm/thp: use head for head page in lru_add_page_tail Alex Shi
2020-11-05 8:55 ` [PATCH v21 03/19] mm/thp: Simplify lru_add_page_tail() Alex Shi
2020-11-05 8:55 ` [PATCH v21 04/19] mm/thp: narrow lru locking Alex Shi
2020-11-05 8:55 ` [PATCH v21 05/19] mm/vmscan: remove unnecessary lruvec adding Alex Shi
2020-11-11 12:36 ` Vlastimil Babka
2020-11-05 8:55 ` [PATCH v21 06/19] mm/rmap: stop store reordering issue on page->mapping Alex Shi
2020-11-06 1:20 ` Alex Shi
2020-11-10 19:06 ` Johannes Weiner
2020-11-11 7:41 ` Hugh Dickins [this message]
2020-11-05 8:55 ` [PATCH v21 07/19] mm: page_idle_get_page() does not need lru_lock Alex Shi
2020-11-10 19:01 ` Johannes Weiner
2020-11-11 8:17 ` huang ying
2020-11-11 12:52 ` Vlastimil Babka
2020-11-05 8:55 ` [PATCH v21 08/19] mm/memcg: add debug checking in lock_page_memcg Alex Shi
2020-11-05 8:55 ` [PATCH v21 09/19] mm/swap.c: fold vm event PGROTATED into pagevec_move_tail_fn Alex Shi
2020-11-05 8:55 ` [PATCH v21 10/19] mm/lru: move lock into lru_note_cost Alex Shi
2020-11-05 8:55 ` [PATCH v21 11/19] mm/vmscan: remove lruvec reget in move_pages_to_lru Alex Shi
2020-11-05 8:55 ` [PATCH v21 12/19] mm/mlock: remove lru_lock on TestClearPageMlocked Alex Shi
2020-11-11 13:03 ` Vlastimil Babka
2020-11-05 8:55 ` [PATCH v21 13/19] mm/mlock: remove __munlock_isolate_lru_page Alex Shi
2020-11-11 13:07 ` Vlastimil Babka
2020-11-05 8:55 ` [PATCH v21 14/19] mm/lru: introduce TestClearPageLRU Alex Shi
2020-11-11 13:36 ` Vlastimil Babka
2020-11-12 2:03 ` Hugh Dickins
2020-11-12 11:24 ` Vlastimil Babka
2020-11-05 8:55 ` [PATCH v21 15/19] mm/compaction: do page isolation first in compaction Alex Shi
2020-11-11 17:12 ` Vlastimil Babka
2020-11-12 2:28 ` Hugh Dickins
2020-11-12 3:35 ` Alex Shi
2020-11-12 11:25 ` Vlastimil Babka
2020-11-05 8:55 ` [PATCH v21 16/19] mm/swap.c: serialize memcg changes in pagevec_lru_move_fn Alex Shi
2020-11-11 18:00 ` Vlastimil Babka
2020-11-05 8:55 ` [PATCH v21 17/19] mm/lru: replace pgdat lru_lock with lruvec lock Alex Shi
2020-11-05 13:43 ` Alex Shi
2020-11-06 7:48 ` Alex Shi
2020-11-10 18:54 ` Johannes Weiner
2020-11-11 17:46 ` Vlastimil Babka
2020-11-11 17:59 ` Vlastimil Babka
2020-11-12 12:19 ` Vlastimil Babka
2020-11-12 14:19 ` Alex Shi
2020-11-05 8:55 ` [PATCH v21 18/19] mm/lru: introduce the relock_page_lruvec function Alex Shi
2020-11-06 7:50 ` Alex Shi
2020-11-10 18:59 ` Johannes Weiner
2020-11-12 12:31 ` Vlastimil Babka
2020-11-05 8:55 ` [PATCH v21 19/19] mm/lru: revise the comments of lru_lock Alex Shi
2020-11-12 12:37 ` Vlastimil Babka
2020-11-10 12:14 ` [PATCH v21 00/19] per memcg lru lock Alex Shi
2020-11-16 3:45 ` Alex Shi
2020-12-15 0:47 ` Andrew Morton
2020-12-15 2:16 ` Hugh Dickins
2020-12-15 2:28 ` Andrew Morton
2021-01-05 19:30 ` Qian Cai
2021-01-05 19:42 ` Shakeel Butt
2021-01-05 20:11 ` Qian Cai
2021-01-05 21:35 ` Hugh Dickins
2021-01-05 22:01 ` Qian Cai
2021-01-06 3:10 ` Hugh Dickins
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