Re: mm: kernel BUG at mm/mlock.c:82!

[Bob Liu <bob.liu@oracle.com>]

cc'd more people.

On 12/17/2013 09:04 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.
> 
> Codewise, it's pretty straightforward. In try_to_unmap_cluster():
> 
>                 page = vm_normal_page(vma, address, *pte);
>                 BUG_ON(!page || PageAnon(page));
> 
>                 if (locked_vma) {
>                         mlock_vma_page(page);   /* no-op if already
> mlocked */
>                         if (page == check_page)
>                                 ret = SWAP_MLOCK;
>                         continue;       /* don't unmap */
>                 }
> 
> And the BUG triggers once we see that 'page' isn't locked.
> 

Yes, I didn't see any place locked the corresponding page in
try_to_unmap_cluster().

I'm afraid adding lock_page() over there may cause potential deadlock.
How about just remove the BUG_ON() in mlock_vma_page()?

> I couldn't find anything that recently changed in those codepaths, so
> I'm a bit lost.
> 
> [  253.869145] kernel BUG at mm/mlock.c:82!
> [  253.869549] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
> [  253.870098] Dumping ftrace buffer:
> [  253.870098]    (ftrace buffer empty)
> [  253.870098] Modules linked in:
> [  253.870098] CPU: 10 PID: 9162 Comm: trinity-child75 Tainted: G       
> W    3.13.0-rc
> 4-next-20131216-sasha-00011-g5f105ec-dirty #4137
> [  253.873310] task: ffff8800c98cb000 ti: ffff8804d34e8000 task.ti:
> ffff8804d34e8000
> [  253.873310] RIP: 0010:[<ffffffff81281f28>]  [<ffffffff81281f28>]
> mlock_vma_page+0x18
> /0xc0
> [  253.873310] RSP: 0000:ffff8804d34e99e8  EFLAGS: 00010246
> [  253.873310] RAX: 006fffff8038002c RBX: ffffea00474944c0 RCX:
> ffff880807636000
> [  253.873310] RDX: ffffea0000000000 RSI: 00007f17a9bca000 RDI:
> ffffea00474944c0
> [  253.873310] RBP: ffff8804d34e99f8 R08: ffff880807020000 R09:
> 0000000000000000
> [  253.873310] R10: 0000000000000001 R11: 0000000000002000 R12:
> 00007f17a9bca000
> [  253.873310] R13: ffffea00474944c0 R14: 00007f17a9be0000 R15:
> ffff880807020000
> [  253.873310] FS:  00007f17aa31a700(0000) GS:ffff8801c9c00000(0000)
> knlGS:000000000000
> 0000
> [  253.873310] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [  253.873310] CR2: 00007f17a94fa000 CR3: 00000004d3b02000 CR4:
> 00000000000006e0
> [  253.873310] DR0: 00007f17a74ca000 DR1: 0000000000000000 DR2:
> 0000000000000000
> [  253.873310] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
> 0000000000000600
> [  253.873310] Stack:
> [  253.873310]  0000000b3de28067 ffff880b3de28e50 ffff8804d34e9aa8
> ffffffff8128bc31
> [  253.873310]  0000000000000301 ffffea0011850220 ffff8809a4039000
> ffffea0011850238
> [  253.873310]  ffff8804d34e9aa8 ffff880807636060 0000000000000001
> ffff880807636348
> [  253.873310] Call Trace:
> [  253.873310]  [<ffffffff8128bc31>] try_to_unmap_cluster+0x1c1/0x340
> [  253.873310]  [<ffffffff8128c60a>] try_to_unmap_file+0x20a/0x2e0
> [  253.873310]  [<ffffffff8128c7b3>] try_to_unmap+0x73/0x90
> [  253.873310]  [<ffffffff812b526d>] __unmap_and_move+0x18d/0x250
> [  253.873310]  [<ffffffff812b53e9>] unmap_and_move+0xb9/0x180
> [  253.873310]  [<ffffffff812b559b>] migrate_pages+0xeb/0x2f0
> [  253.873310]  [<ffffffff812a0660>] ? queue_pages_pte_range+0x1a0/0x1a0
> [  253.873310]  [<ffffffff812a193c>] migrate_to_node+0x9c/0xc0
> [  253.873310]  [<ffffffff812a30b8>] do_migrate_pages+0x1b8/0x240
> [  253.873310]  [<ffffffff812a3456>] SYSC_migrate_pages+0x316/0x380
> [  253.873310]  [<ffffffff812a31ec>] ? SYSC_migrate_pages+0xac/0x380
> [  253.873310]  [<ffffffff811763c6>] ? vtime_account_user+0x96/0xb0
> [  253.873310]  [<ffffffff812a34ce>] SyS_migrate_pages+0xe/0x10
> [  253.873310]  [<ffffffff843c4990>] tracesys+0xdd/0xe2
> [  253.873310] Code: 0f 1f 00 65 48 ff 04 25 10 25 1d 00 48 83 c4 08 5b
> c9 c3 55 48 89 e5 53 48 83 ec 08 66 66 66 66 90 48 8b 07 48 89 fb a8 01
> 75 10 <0f> 0b 66 0f 1f 44 00 00 eb fe 66 0f 1f 44 00 00 f0 0f ba 2f 15
> [  253.873310] RIP  [<ffffffff81281f28>] mlock_vma_page+0x18/0xc0
> [  253.873310]  RSP <ffff8804d34e99e8>
> [  253.904194] ---[ end trace be59c4a7f8edab3f ]---
> 
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-- 
Regards,
-Bob

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