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Date:	Thu, 26 Sep 2013 09:59:24 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Bob Liu <bob.liu@...cle.com>
Cc:	Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [munlock] BUG: Bad page map in process killall5 pte:cf17e720
 pmd:05a22067

Hi Bob,

On Thu, Sep 26, 2013 at 09:48:08AM +0800, Bob Liu wrote:
> Hi Fengguang,
> 
> Would you please have a try with the attached patch?
> It added a small fix based on Vlastimil's patch.

Thanks for the quick response! I just noticed Andrew added this patch
to -mm tree:

------------------------------------------------------
From: Vlastimil Babka <vbabka@...e.cz>
Subject: mm/mlock.c: prevent walking off the end of a pagetable in no-pmd configuration

What's the git tree your v2 patch based on? If you already had a git
tree, it'd be more simple to push it to a branch and tell me the
tree/branch/commit to test.

Thanks,
Fengguang

> 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@...e.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@...e.cz>
> >     Cc: Jörn Engel <joern@...fs.org>
> >     Cc: Mel Gorman <mgorman@...e.de>
> >     Cc: Michel Lespinasse <walken@...gle.com>
> >     Cc: Hugh Dickins <hughd@...gle.com>
> >     Cc: Rik van Riel <riel@...hat.com>
> >     Cc: Johannes Weiner <hannes@...xchg.org>
> >     Cc: Michal Hocko <mhocko@...e.cz>
> >     Cc: Vlastimil Babka <vbabka@...e.cz>
> >     Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> >     Signed-off-by: Linus Torvalds <torvalds@...ux-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
> > 

> >From aef673d802a92aef8dc082c244fef51ae9c4a13c Mon Sep 17 00:00:00 2001
> From: Bob Liu <bob.liu@...cle.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@...el.com>
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> Signed-off-by: Bob Liu <bob.liu@...cle.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
> 

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