The patch titled
Subject: mm/rmap: stop store reordering issue on page->mapping
has been removed from the -mm tree. Its filename was
mm-rmap-stop-store-reordering-issue-on-page-mapping.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
Subject: 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."
[alex.shi@xxxxxxxxxxxxxxxxx: updated for comments change from Johannes]
Link: https://lkml.kernel.org/r/e66ef2e5-c74c-6498-e8b3-56c37b9d2d15@xxxxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/1604566549-62481-7-git-send-email-alex.shi@xxxxxxxxxxxxxxxxx
Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Alexander Duyck <alexander.duyck@xxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: "Chen, Rong A" <rong.a.chen@xxxxxxxxx>
Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
Cc: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mika Penttilä <mika.penttila@xxxxxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Wei Yang <richard.weiyang@xxxxxxxxx>
Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/rmap.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
--- a/mm/rmap.c~mm-rmap-stop-store-reordering-issue-on-page-mapping
+++ a/mm/rmap.c
@@ -1054,8 +1054,14 @@ static void __page_set_anon_rmap(struct
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);
}
_
Patches currently in -mm which might be from alex.shi@xxxxxxxxxxxxxxxxx are
mm-vmscan-__isolate_lru_page_prepare-clean-up.patch
fs-nilfs2-remove-some-unused-macros-to-tame-gcc.patch
gcov-fix-kernel-doc-markup-issue.patch
mm-memcg-bail-early-from-swap-accounting-if-memcg-disabled.patch
mm-memcg-warning-on-memcg-after-readahead-page-charged.patch
mm-memcontrol-rewrite-mem_cgroup_page_lruvec-fix.patch
