mm: kernel BUG at include/linux/swapops.h:131!

[Sasha Levin]

Hi all,

While fuzzing with trinity inside a KVM tools guest running latest -next kernel, I've stumbled on 
the following spew.

The code is in zap_pte_range():

                if (!non_swap_entry(entry))
                        rss[MM_SWAPENTS]--;
                else if (is_migration_entry(entry)) {
                        struct page *page;

                        page = migration_entry_to_page(entry);	<==== HERE

                        if (PageAnon(page))
                                rss[MM_ANONPAGES]--;
                        else
                                rss[MM_FILEPAGES]--;


[ 2622.589064] kernel BUG at include/linux/swapops.h:131!
[ 2622.589064] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[ 2622.589064] Dumping ftrace buffer:
[ 2622.589064]    (ftrace buffer empty)
[ 2622.589064] Modules linked in:
[ 2622.589064] CPU: 9 PID: 15984 Comm: trinity-child16 Tainted: G        W    3.13.0-rc
4-next-20131217-sasha-00013-ga878504-dirty #4150
[ 2622.589064] task: ffff88168346b000 ti: ffff8816561d8000 task.ti: ffff8816561d8000
[ 2622.589064] RIP: 0010:[<ffffffff8127c730>]  [<ffffffff8127c730>] zap_pte_range+0x360
/0x4a0
[ 2622.589064] RSP: 0018:ffff8816561d9c18  EFLAGS: 00010246
[ 2622.589064] RAX: ffffea00736a6600 RBX: ffff88200299d068 RCX: 0000000000000009
[ 2622.589064] RDX: 022fffff80380000 RSI: ffffea0000000000 RDI: 3c00000001cda998
[ 2622.589064] RBP: ffff8816561d9cb8 R08: 0000000000000000 R09: 0000000000000000
[ 2622.589064] R10: 0000000000000001 R11: 0000000000000000 R12: 00007fc7ee20d000
[ 2622.589064] R13: ffff8816561d9de8 R14: 000000039b53303c R15: 00007fc7ee29b000
[ 2622.589064] FS:  00007fc7eeceb700(0000) GS:ffff882011a00000(0000) knlGS:000000000000
0000
[ 2622.589064] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 2622.589064] CR2: 000000000068c000 CR3: 0000000005c26000 CR4: 00000000000006e0
[ 2622.589064] Stack:
[ 2622.589064]  ffff8816561d9c58 0000000000000286 ffff88168327b060 ffff88168327b060
[ 2622.589064]  00007fc700000160 ffff881667067b88 00000000c8f4b120 00ff88168327b060
[ 2622.589064]  ffff88168327b060 ffff8820051a8600 0000000000000000 ffff88168327b000
[ 2622.589064] Call Trace:
[ 2622.589064]  [<ffffffff8127cc5e>] unmap_page_range+0x3ee/0x400
[ 2622.589064]  [<ffffffff8127cd71>] unmap_single_vma+0x101/0x120
[ 2622.589064]  [<ffffffff8127cdf1>] unmap_vmas+0x61/0xa0
[ 2622.589064]  [<ffffffff81283980>] exit_mmap+0xd0/0x170
[ 2622.589064]  [<ffffffff8112d430>] mmput+0x70/0xe0
[ 2622.589064]  [<ffffffff8113144d>] exit_mm+0x18d/0x1a0
[ 2622.589064]  [<ffffffff811defb5>] ? acct_collect+0x175/0x1b0
[ 2622.589064]  [<ffffffff8113389f>] do_exit+0x24f/0x500
[ 2622.589064]  [<ffffffff81133bf9>] do_group_exit+0xa9/0xe0
[ 2622.589064]  [<ffffffff81133c47>] SyS_exit_group+0x17/0x20
[ 2622.589064]  [<ffffffff843a6150>] tracesys+0xdd/0xe2
[ 2622.589064] Code: 83 f8 1f 75 46 48 b8 ff ff ff ff ff ff ff 01 48 be 00 00 00 00 00 ea ff ff 48 
21 f8 48 c1 e0 06 48 01 f0 48 8b 10 80 e2 01 75 0a <0f> 0b 66 0f 1f 44 00 00 eb fe f6 40 08 01 74 05 
ff 4d c4 eb 0b
[ 2622.589064] RIP  [<ffffffff8127c730>] zap_pte_range+0x360/0x4a0
[ 2622.589064]  RSP <ffff8816561d9c18>
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