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Date:	Sat, 29 Mar 2014 20:47:15 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Bob Liu <bob.liu@...cle.com>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: mm: kernel BUG at mm/swap.c:609!

On 03/20/2014 05:21 AM, Bob Liu wrote:
>
> On 03/12/2014 09:25 AM, Bob Liu wrote:
>>
>> On 03/12/2014 04:07 AM, Sasha Levin wrote:
>>> Hi all,
>>>
>>> While fuzzing with trinity inside a KVM tools guest running latest -next
>>> kernel
>>> I've stumbled on the following spew:
>>>
>>> [  477.301955] kernel BUG at mm/swap.c:609!
>>> [  477.302564] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
>>> [  477.303590] Dumping ftrace buffer:
>>> [  477.305022]    (ftrace buffer empty)
>>> [  477.305899] Modules linked in:
>>> [  477.306397] CPU: 35 PID: 10092 Comm: trinity-c374 Tainted: G
>>> W    3.14.0-rc5-next-20140307-sasha-00010-g1f812cb #142
>>> [  477.307644] task: ffff8800a7f80000 ti: ffff8800a7f6a000 task.ti:
>>> ffff8800a7f6a000
>>> [  477.309124] RIP: 0010:[<ffffffff8127f311>]  [<ffffffff8127f311>]
>>> lru_cache_add+0x21/0x60
>>> [  477.310301] RSP: 0000:ffff8800a7f6bbc8  EFLAGS: 00010292
>>> [  477.311110] RAX: 000000000000003f RBX: ffffea0013d68000 RCX:
>>> 0000000000000006
>>> [  477.311110] RDX: 0000000000000006 RSI: ffff8800a7f80d60 RDI:
>>> 0000000000000282
>>> [  477.311110] RBP: ffff8800a7f6bbc8 R08: 0000000000000001 R09:
>>> 0000000000000001
>>> [  477.311110] R10: 0000000000000001 R11: 0000000000000001 R12:
>>> ffff8800ab9b0c00
>>> [  477.311110] R13: 0000000002400000 R14: ffff8800ab9b0c00 R15:
>>> 0000000000000001
>>> [  477.311110] FS:  00007ff2c047c700(0000) GS:ffff88042bc00000(0000)
>>> knlGS:0000000000000000
>>> [  477.311110] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>>> [  477.311110] CR2: 0000000003788a68 CR3: 00000000a7f68000 CR4:
>>> 00000000000006a0
>>> [  477.311110] DR0: 000000000069b000 DR1: 0000000000000000 DR2:
>>> 0000000000000000
>>> [  477.311110] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
>>> 0000000000000600
>>> [  477.311110] Stack:
>>> [  477.311110]  ffff8800a7f6bbf8 ffffffff812adaec ffffea0013d68000
>>> ffffea002bdb8000
>>> [  477.311110]  ffffea0013d68000 ffff8800a7f7c090 ffff8800a7f6bca8
>>> ffffffff812db8ec
>>> [  477.311110]  0000000000000001 ffffffff812e1321 ffff8800a7f6bc48
>>> ffffffff811ad632
>>> [  477.311110] Call Trace:
>>> [  477.311110]  [<ffffffff812adaec>] page_add_new_anon_rmap+0x1ec/0x210
>>> [  477.311110]  [<ffffffff812db8ec>]
>>> migrate_misplaced_transhuge_page+0x55c/0x830
>>> [  477.311110]  [<ffffffff812e1321>] ? do_huge_pmd_numa_page+0x311/0x460
>>> [  477.311110]  [<ffffffff811ad632>] ? __lock_release+0x1e2/0x200
>>> [  477.311110]  [<ffffffff812e133f>] do_huge_pmd_numa_page+0x32f/0x460
>>> [  477.311110]  [<ffffffff81af6aca>] ? delay_tsc+0xfa/0x120
>>> [  477.311110]  [<ffffffff812a31f4>] __handle_mm_fault+0x244/0x3a0
>>> [  477.311110]  [<ffffffff812e37ed>] ? rcu_read_unlock+0x5d/0x60
>>> [  477.311110]  [<ffffffff812a3463>] handle_mm_fault+0x113/0x1c0
>>> [  477.311110]  [<ffffffff844abd42>] ? __do_page_fault+0x302/0x5d0
>>> [  477.311110]  [<ffffffff844abfd1>] __do_page_fault+0x591/0x5d0
>>> [  477.311110]  [<ffffffff8118ab46>] ? vtime_account_user+0x96/0xb0
>>> [  477.311110]  [<ffffffff844ac492>] ? preempt_count_sub+0xe2/0x120
>>> [  477.311110]  [<ffffffff81269567>] ?
>>> context_tracking_user_exit+0x187/0x1d0
>>> [  477.311110]  [<ffffffff844ac0d5>] do_page_fault+0x45/0x70
>>> [  477.311110]  [<ffffffff844ab386>] do_async_page_fault+0x36/0x100
>>> [  477.311110]  [<ffffffff844a7f18>] async_page_fault+0x28/0x30
>>> [  477.311110] Code: 65 f0 4c 8b 6d f8 c9 c3 66 90 55 48 89 e5 66 66 66
>>> 66 90 48 8b 07 a8 40 74 18 48 8b 07 a9 00 00 10 00 74 0e 31 f6 e8 2f 20
>>> ff ff <0f> 0b eb fe 0f 1f 00 48 8b 07 a8 20 74 19 31 f6 e8 1a 20 ff ff
>>> [  477.311110] RIP  [<ffffffff8127f311>] lru_cache_add+0x21/0x60
>>> [  477.311110]  RSP <ffff8800a7f6bbc8>
>>>
>>
>>
>> If PageUnevictable(old_page) is true, new page will also be set before
>> page_add_new_anon_rmap().
>>
>> migrate_misplaced_transhuge_page()
>>      > migrate_page_copy()
>>          > SetPageUnevictable(newpage)
>>      > page_add_new_anon_rmap()
>>
>> But in page_add_new_anon_rmap(), there is only mlocked_vma_newpage()
>> called to check whether a page should be added to unevictable list. I
>> think that is incorrect in some cases and may trigger this BUG().
>>
>> We can see from vmscan:
>> int page_evictable(struct page *page)
>> {
>>      return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
>> }
>>
>> Besides mlock, we may also set a page to unevictable when that page's
>> mapping marked unevictable.
>>
>> mlocked_vma_newpage(new_page) can't detect this situation if the old
>> page is set to unevictable by this reason. So I think we should add an
>> extra !PageUnevictable(page) checking in page_add_new_anon_rmap().
>> Fix me if I misunderstood something.
>>
>> diff --git a/mm/rmap.c b/mm/rmap.c
>> index 9056a1f..8d13318 100644
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -1024,7 +1024,7 @@ void page_add_new_anon_rmap(struct page *page,
>>          __mod_zone_page_state(page_zone(page), NR_ANON_PAGES,
>>                          hpage_nr_pages(page));
>>          __page_set_anon_rmap(page, vma, address, 1);
>> -       if (!mlocked_vma_newpage(vma, page)) {
>> +       if (!mlocked_vma_newpage(vma, page) && !PageUnevictable(page)) {
>>                  SetPageActive(page);
>>                  lru_cache_add(page);
>>          } else
>>
>>
>
> Sasha, any lucky with above changes? If it can fix this issue, I'll
> resend out a patch.

I've been running with it for a while and haven't seen the issue reproduce,
looks good to me.


Thanks,
Sasha

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