The patch titled Subject: mm/compaction: avoid VM_BUG_ON(PageSlab()) in page_mapcount() has been removed from the -mm tree. Its filename was mm-compaction-avoid-vm_bug_onpageslab-in-page_mapcount.patch
This patch was dropped because it is obsolete
------------------------------------------------------ From: Konstantin Khlebnikov khlebnikov@yandex-team.ru Subject: mm/compaction: avoid VM_BUG_ON(PageSlab()) in page_mapcount()
isolate_migratepages_block() runs some checks out of lru_lock when choosing pages for migration. After checking PageLRU() it checks extra page references by comparing page_count() and page_mapcount(). Between these two checks page could be removed from lru, freed and taken by slab.
As a result this race triggers VM_BUG_ON(PageSlab()) in page_mapcount(). Race window is tiny. For certain workload this happens around once a year.
page:ffffea0105ca9380 count:1 mapcount:0 mapping:ffff88ff7712c180 index:0x0 compound_mapcount: 0 flags: 0x500000000008100(slab|head) raw: 0500000000008100 dead000000000100 dead000000000200 ffff88ff7712c180 raw: 0000000000000000 0000000080200020 00000001ffffffff 0000000000000000 page dumped because: VM_BUG_ON_PAGE(PageSlab(page)) ------------[ cut here ]------------ kernel BUG at ./include/linux/mm.h:628! invalid opcode: 0000 [#1] SMP NOPTI CPU: 77 PID: 504 Comm: kcompactd1 Tainted: G W 4.19.109-27 #1 Hardware name: Yandex T175-N41-Y3N/MY81-EX0-Y3N, BIOS R05 06/20/2019 RIP: 0010:isolate_migratepages_block+0x986/0x9b0
To fix just opencode page_mapcount() in racy check for 0-order case and recheck carefully under lru_lock when page cannot escape from lru.
Also add checking extra references for file pages and swap cache.
Link: http://lkml.kernel.org/r/158937872515.474360.5066096871639561424.stgit@buzz Fixes: 119d6d59dcc0 ("mm, compaction: avoid isolating pinned pages") Fixes: 1d148e218a0d ("mm: add VM_BUG_ON_PAGE() to page_mapcount()") Signed-off-by: Konstantin Khlebnikov khlebnikov@yandex-team.ru Cc: Minchan Kim minchan@kernel.org Cc: Vlastimil Babka vbabka@suse.cz Cc: David Rientjes rientjes@google.com Cc: Mel Gorman mgorman@techsingularity.net Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/compaction.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-)
--- a/mm/compaction.c~mm-compaction-avoid-vm_bug_onpageslab-in-page_mapcount +++ a/mm/compaction.c @@ -935,12 +935,16 @@ isolate_migratepages_block(struct compac }
/* - * Migration will fail if an anonymous page is pinned in memory, + * Migration will fail if an page is pinned in memory, * so avoid taking lru_lock and isolating it unnecessarily in an - * admittedly racy check. + * admittedly racy check simplest case for 0-order pages. + * + * Open code page_mapcount() to avoid VM_BUG_ON(PageSlab(page)). + * Page could have extra reference from mapping or swap cache. */ - if (!page_mapping(page) && - page_count(page) > page_mapcount(page)) + if (!PageCompound(page) && + page_count(page) > atomic_read(&page->_mapcount) + 1 + + (!PageAnon(page) || PageSwapCache(page))) goto isolate_fail;
/* @@ -975,6 +979,11 @@ isolate_migratepages_block(struct compac low_pfn += compound_nr(page) - 1; goto isolate_fail; } + + /* Recheck page extra references under lock */ + if (page_count(page) > page_mapcount(page) + + (!PageAnon(page) || PageSwapCache(page))) + goto isolate_fail; }
lruvec = mem_cgroup_page_lruvec(page, pgdat); _
Patches currently in -mm which might be from khlebnikov@yandex-team.ru are
kernel-watchdog-flush-all-printk-nmi-buffers-when-hardlockup-detected.patch doc-cgroup-update-note-about-conditions-when-oom-killer-is-invoked.patch