From: Andrew Morton <akpm@linux-foundation.org>
To: akpm@linux-foundation.org, hughd@google.com,
khlebnikov@yandex-team.ru, kirill.shutemov@linux.intel.com,
linux-mm@kvack.org, mm-commits@vger.kernel.org,
rientjes@google.com, stable@vger.kernel.org,
torvalds@linux-foundation.org, vbabka@suse.cz
Subject: [patch 3/5] mm: remove VM_BUG_ON(PageSlab()) from page_mapcount()
Date: Wed, 27 May 2020 22:20:47 -0700 [thread overview]
Message-ID: <20200528052047.tDxIOLXzt%akpm@linux-foundation.org> (raw)
In-Reply-To: <20200527222015.62ba8592af63dae12ab58ffe@linux-foundation.org>
From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Subject: mm: remove VM_BUG_ON(PageSlab()) from page_mapcount()
Replace superfluous VM_BUG_ON() with comment about correct usage.
Technically reverts commit 1d148e218a0d0566b1c06f2f45f1436d53b049b2
("mm: add VM_BUG_ON_PAGE() to page_mapcount()"), but context have changed.
Function isolate_migratepages_block() runs some checks out of lru_lock
when choose 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
Code in isolate_migratepages_block() was added in commit 119d6d59dcc0
("mm, compaction: avoid isolating pinned pages") before adding VM_BUG_ON
into page_mapcount().
This race has been predicted in 2015 by Vlastimil Babka (see link below).
[akpm@linux-foundation.org: comment tweaks, per Hugh]
Link: http://lkml.kernel.org/r/159032779896.957378.7852761411265662220.stgit@buzz
Link: https://lore.kernel.org/lkml/557710E1.6060103@suse.cz/
Link: https://lore.kernel.org/linux-mm/158937872515.474360.5066096871639561424.stgit@buzz/T/ (v1)
Fixes: 1d148e218a0d ("mm: add VM_BUG_ON_PAGE() to page_mapcount()")
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Acked-by: Hugh Dickins <hughd@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
include/linux/mm.h | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)
--- a/include/linux/mm.h~mm-remove-vm_bug_onpageslab-from-page_mapcount
+++ a/include/linux/mm.h
@@ -782,6 +782,11 @@ static inline void *kvcalloc(size_t n, s
extern void kvfree(const void *addr);
+/*
+ * Mapcount of compound page as a whole, does not include mapped sub-pages.
+ *
+ * Must be called only for compound pages or any their tail sub-pages.
+ */
static inline int compound_mapcount(struct page *page)
{
VM_BUG_ON_PAGE(!PageCompound(page), page);
@@ -801,10 +806,16 @@ static inline void page_mapcount_reset(s
int __page_mapcount(struct page *page);
+/*
+ * Mapcount of 0-order page; when compound sub-page, includes
+ * compound_mapcount().
+ *
+ * Result is undefined for pages which cannot be mapped into userspace.
+ * For example SLAB or special types of pages. See function page_has_type().
+ * They use this place in struct page differently.
+ */
static inline int page_mapcount(struct page *page)
{
- VM_BUG_ON_PAGE(PageSlab(page), page);
next prev parent reply other threads:[~2020-05-28 5:20 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-28 5:20 incoming Andrew Morton
2020-05-28 5:20 ` [patch 1/5] mm/z3fold: silence kmemleak false positives of slots Andrew Morton
2020-05-28 5:20 ` [patch 2/5] mm,thp: stop leaking unreleased file pages Andrew Morton
2020-05-28 5:20 ` Andrew Morton [this message]
2020-05-28 5:20 ` [patch 4/5] fs/binfmt_elf.c: allocate initialized memory in fill_thread_core_info() Andrew Morton
2020-05-28 5:20 ` [patch 5/5] include/asm-generic/topology.h: guard cpumask_of_node() macro argument Andrew Morton
2020-05-28 19:11 ` [alternative-merged] add-kernel-config-option-for-twisting-kernel-behavior.patch removed from -mm tree Andrew Morton
2020-05-28 19:11 ` [alternative-merged] twist-allow-disabling-k_spec-function-in-drivers-tty-vt-keyboardc.patch " Andrew Morton
2020-05-28 19:11 ` [alternative-merged] twist-add-option-for-selecting-twist-options-for-syzkallers-testing.patch " Andrew Morton
[not found] ` <CAHk-=whQSWcE1WvKxptHdyc9BUXQyxxyAH954=Jb_YSBrNJYDQ@mail.gmail.com>
2020-05-29 20:31 ` incoming Andrew Morton
[not found] ` <CAHk-=wiU-vQVURz62dzitbh2Pk+m_+ipaJU6=z=ES3cd_wKSLQ@mail.gmail.com>
2020-05-29 21:12 ` incoming Andrew Morton
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