Re: [munlock] BUG: Bad page map in process killall5 pte:cf17e720 pmd:05a22067

Bob Liu
2013-09-26T01:48:22Z

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Hi Fengguang,

Would you please have a try with the attached patch?
It added a small fix based on Vlastimil's patch.

Thanks,
-Bob

On 09/26/2013 08:40 AM, Fengguang Wu wrote:
> Hi Vlastimil,
>
> FYI, this bug seems still not fixed in linux-next 20130925.
>
> commit 7a8010cd36273ff5f6fea5201ef9232f30cebbd9
> Author: Vlastimil Babka <vbabka@suse.cz>
> Date: Wed Sep 11 14:22:35 2013 -0700
>
> mm: munlock: manual pte walk in fast path instead of follow_page_mask()
>
> Currently munlock_vma_pages_range() calls follow_page_mask() to obtain
> each individual struct page. This entails repeated full page table
> translations and page table lock taken for each page separately.
>
> This patch avoids the costly follow_page_mask() where possible, by
> iterating over ptes within single pmd under single page table lock. The
> first pte is obtained by get_locked_pte() for non-THP page acquired by the
> initial follow_page_mask(). The rest of the on-stack pagevec for munlock
> is filled up using pte_walk as long as pte_present() and vm_normal_page()
> are sufficient to obtain the struct page.
>
> After this patch, a 14% speedup was measured for munlocking a 56GB large
> memory area with THP disabled.
>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> Cc: Jörn Engel <joern@logfs.org>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Michel Lespinasse <walken@google.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@suse.cz>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
>
>
> [ 89.835504] init: plymouth-upstart-bridge main process (3556) terminated with status 1
> [ 89.986606] init: tty6 main process (3529) killed by TERM signal
> [ 91.414086] BUG: Bad page map in process killall5 pte:cf17e720 pmd:05a22067
> [ 91.416626] addr:bfc00000 vm_flags:00100173 anon_vma:cf128c80 mapping: (null) index:bfff0
> [ 91.419402] CPU: 0 PID: 3574 Comm: killall5 Not tainted 3.12.0-rc1-00010-g5fbc0a6 #24
> [ 91.422171] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> [ 91.423998] 00000000 00000000 c0199e34 c1db5db4 00000000 c0199e54 c10e72d4 000bfff0
> [ 91.427933] 00000000 bfc00000 00000000 000cf17e cf17e720 c0199e74 c10e7995 00000000
> [ 91.431940] bfc00000 cf1ca190 bfc00000 cf180000 cf1ca190 c0199ee0 c10eb8cf ce6d1900
> [ 91.435894] Call Trace:
> [ 91.436969] [<c1db5db4>] dump_stack+0x4b/0x66
> [ 91.438503] [<c10e72d4>] print_bad_pte+0x14b/0x162
> [ 91.440204] [<c10e7995>] vm_normal_page+0x67/0x9b
> [ 91.441811] [<c10eb8cf>] munlock_vma_pages_range+0xf9/0x176
> [ 91.443633] [<c10ede09>] exit_mmap+0x86/0xf7
> [ 91.445156] [<c10885b8>] ? lock_release+0x169/0x1ef
> [ 91.446795] [<c113e5b6>] ? rcu_read_unlock+0x17/0x23
> [ 91.448465] [<c113effe>] ? exit_aio+0x2b/0x6c
> [ 91.449990] [<c103d4b0>] mmput+0x6a/0xcb
> [ 91.451508] [<c104141a>] do_exit+0x362/0x8be
> [ 91.453013] [<c105d280>] ? hrtimer_debug_hint+0xd/0xd
> [ 91.454700] [<c10419f8>] do_group_exit+0x51/0x9e
> [ 91.456296] [<c1041a5b>] SyS_exit_group+0x16/0x16
> [ 91.457901] [<c1dc6719>] sysenter_do_call+0x12/0x33
> [ 91.459553] Disabling lock debugging due to kernel taint
>
> git bisect start 272b98c6455f00884f0350f775c5342358ebb73f v3.11 --
> git bisect good 57d730924d5cc2c3e280af16a9306587c3a511db # 02:21 495+ Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
> git bisect good 3bb22ec53e2bd12a241ed84359bffd591a40ab87 # 12:03 495+ staging/lustre/ptlrpc: convert to new shrinker API
> git bisect bad a5b7c87f92076352dbff2fe0423ec255e1c9a71b # 12:18 31- vmscan, memcg: do softlimit reclaim also for targeted reclaim
> git bisect good 3d94ea51c1d8db6f41268a9d2aea5f5771e9a8d3 # 15:40 495+ ocfs2: clean up dead code in ocfs2_acl_from_xattr()
> git bisect bad d62a201f24cba74e2fbf9f6f7af86ff5f5e276fc # 16:46 79- checkpatch: enforce sane perl version
> git bisect good 83467efbdb7948146581a56cbd683a22a0684bbb # 01:29 585+ mm: migrate: check movability of hugepage in unmap_and_move_huge_page()
> git bisect bad 2bff24a3707093c435ab3241c47dcdb5f16e432b # 02:07 148- memcg: fix multiple large threshold notifications
> git bisect bad 1ecfd533f4c528b0b4cc5bc115c4c47f0b5e4828 # 02:34 64- mm/mremap.c: call pud_free() after fail calling pmd_alloc()
> git bisect good 0ec3b74c7f5599c8a4d2b33d430a5470af26ebf6 # 13:10 1170+ mm: putback_lru_page: remove unnecessary call to page_lru_base_type()
> git bisect good 5b40998ae35cf64561868370e6c9f3d3e94b6bf7 # 16:52 1170+ mm: munlock: remove redundant get_page/put_page pair on the fast path
> git bisect bad 187320932dcece9c4b93f38f56d1f888bd5c325f # 17:11 0- mm/sparse: introduce alloc_usemap_and_memmap
> git bisect bad 6e543d5780e36ff5ee56c44d7e2e30db3457a7ed # 17:29 2- mm: vmscan: fix do_try_to_free_pages() livelock
> git bisect bad 7a8010cd36273ff5f6fea5201ef9232f30cebbd9 # 17:59 14- mm: munlock: manual pte walk in fast path instead of follow_page_mask()
> git bisect good 5b40998ae35cf64561868370e6c9f3d3e94b6bf7 # 22:10 3510+ mm: munlock: remove redundant get_page/put_page pair on the fast path
> git bisect bad 5fbc0a6263a147cde905affbfb6622c26684344f # 22:10 0- Merge remote-tracking branch 'pinctrl/for-next' into kbuild_tmp
> git bisect good 87e37036dcf96eb73a8627524be8b722bd1ac526 # 04:31 3510+ Revert "mm: munlock: manual pte walk in fast path instead of follow_page_mask()"
> git bisect bad 22356f447ceb8d97a4885792e7d9e4607f712e1b # 04:40 48- mm: Place preemption point in do_mlockall() loop
> git bisect bad 050f4da86e9bdbcc9e11789e0f291aafa57b8a20 # 04:55 133- Add linux-next specific files for 20130925
>
> Thanks,
> Fengguang
>

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>From aef673d802a92aef8dc082c244fef51ae9c4a13c Mon Sep 17 00:00:00 2001
From: Bob Liu <bob.liu@oracle.com>
Date: Thu, 26 Sep 2013 09:41:27 +0800
Subject: [PATCH v2] mm: munlock: Prevent walking off the end of a pagetable in
no-pmd configuration

The function __munlock_pagevec_fill() introduced in commit 7a8010cd3
("mm: munlock: manual pte walk in fast path instead of follow_page_mask()")
uses pmd_addr_end() for restricting its operation within current page table.
This is insufficient on architectures/configurations where pmd is folded
and pmd_addr_end() just returns the end of the full range to be walked. In
this case, it allows pte++ to walk off the end of a page table resulting in
unpredictable behaviour.

This patch fixes the function by using pgd_addr_end() and pud_addr_end()
before pmd_addr_end(), which will yield correct page table boundary on all
configurations. This is similar to what existing page walkers do when walking
each level of the page table.

Additionaly, the patch clarifies a comment for get_locked_pte() call in the
function.

v2: walk page table after start += PAGESIZE

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Bob Liu <bob.liu@oracle.com>
---
mm/mlock.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/mm/mlock.c b/mm/mlock.c
index d638026..a91114a 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -379,13 +379,19 @@ static unsigned long __munlock_pagevec_fill(struct pagevec *pvec,

/*
* Initialize pte walk starting at the already pinned page where we
- * are sure that there is a pte.
+ * are sure that there is a pte, as it was pinned under the same
+ * mmap_sem write op.
*/
pte = get_locked_pte(vma->vm_mm, start, &ptl);
- end = min(end, pmd_addr_end(start, end));

/* The page next to the pinned page is the first we will try to get */
start += PAGE_SIZE;
+
+ /* Make sure we do not cross the page table boundary */
+ end = pgd_addr_end(start, end);
+ end = pud_addr_end(start, end);
+ end = pmd_addr_end(start, end);
+
while (start < end) {
struct page *page = NULL;
pte++;
--
1.7.10.4