From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: + mm-compaction-avoid-vm_bug_onpageslab-in-page_mapcount.patch added to -mm tree Date: Wed, 13 May 2020 11:31:38 -0700 Message-ID: <20200513183138.3e12_5I1z%akpm@linux-foundation.org> References: <20200507183509.c5ef146c5aaeb118a25a39a8@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:48226 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390151AbgEMSbl (ORCPT ); Wed, 13 May 2020 14:31:41 -0400 In-Reply-To: <20200507183509.c5ef146c5aaeb118a25a39a8@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: khlebnikov@yandex-team.ru, mgorman@techsingularity.net, minchan@kernel.org, mm-commits@vger.kernel.org, rientjes@google.com, vbabka@suse.cz The patch titled Subject: mm/compaction: avoid VM_BUG_ON(PageSlab()) in page_mapcount() has been added to the -mm tree. Its filename is mm-compaction-avoid-vm_bug_onpageslab-in-page_mapcount.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-compaction-avoid-vm_bug_onpageslab-in-page_mapcount.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-compaction-avoid-vm_bug_onpageslab-in-page_mapcount.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Konstantin Khlebnikov 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 Cc: Minchan Kim Cc: Vlastimil Babka Cc: David Rientjes Cc: Mel Gorman Signed-off-by: Andrew Morton --- 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 mm-compaction-avoid-vm_bug_onpageslab-in-page_mapcount.patch kernel-watchdog-flush-all-printk-nmi-buffers-when-hardlockup-detected.patch doc-cgroup-update-note-about-conditions-when-oom-killer-is-invoked.patch