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Date:	Wed, 12 Mar 2014 09:25:18 +0800
From:	Bob Liu <bob.liu@...cle.com>
To:	Sasha Levin <sasha.levin@...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 03/12/2014 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


-- 
Regards,
--Bob

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