mm: kernel BUG at mm/huge_memory.c:1440!

[Sasha Levin]

Hi all,

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

	page = pmd_page(orig_pmd);
	page_remove_rmap(page);
	VM_BUG_ON(page_mapcount(page) < 0);
	add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
	VM_BUG_ON(!PageHead(page));		<=== HERE
	atomic_long_dec(&tlb->mm->nr_ptes);
	spin_unlock(ptl);
	tlb_remove_page(tlb, page);

[  265.474585] kernel BUG at mm/huge_memory.c:1440!
[  265.475129] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[  265.476684] Dumping ftrace buffer:
[  265.477144]    (ftrace buffer empty)
[  265.478398] Modules linked in:
[  265.478807] CPU: 8 PID: 11344 Comm: trinity-c206 Tainted: G        W    3.13.0-rc5-ne
xt-20131223-sasha-00015-gec22156-dirty #8
[  265.480172] task: ffff8801cb573000 ti: ffff8801cbd3a000 task.ti: ffff8801cbd3a000
[  265.480172] RIP: 0010:[<ffffffff812c7f70>]  [<ffffffff812c7f70>] zap_huge_pmd+0x170/0
x1f0
[  265.480172] RSP: 0000:ffff8801cbd3bc78  EFLAGS: 00010246
[  265.480172] RAX: 015fffff80090018 RBX: ffff8801cbd3bde8 RCX: ffffffffffffff9c
[  265.480172] RDX: ffffffffffffffff RSI: 0000000000000008 RDI: ffff8800bffd2000
[  265.480172] RBP: ffff8801cbd3bcb8 R08: 0000000000000000 R09: 0000000000000000
[  265.480172] R10: 0000000000000001 R11: 0000000000000000 R12: ffffea0002856740
[  265.480172] R13: ffffea0002d50000 R14: 00007ff915000000 R15: 00007ff930e48fff
[  265.480172] FS:  00007ff934899700(0000) GS:ffff88014d400000(0000) knlGS:0000000000000
000
[  265.480172] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  265.480172] CR2: 00007ff93428a000 CR3: 000000010babe000 CR4: 00000000000006e0
[  265.480172] Stack:
[  265.480172]  00000000000004dd ffff8801ccbfbb60 ffff8801cbd3bcb8 ffff8801cbb15540
[  265.480172]  00007ff915000000 00007ff930e49000 ffff8801cbd3bde8 00007ff930e48fff
[  265.480172]  ffff8801cbd3bd48 ffffffff812885b6 ffff88005f5d20c0 00007ff915200000
[  265.480172] Call Trace:
[  265.480172]  [<ffffffff812885b6>] unmap_page_range+0x2c6/0x410
[  265.480172]  [<ffffffff81288801>] unmap_single_vma+0x101/0x120
[  265.480172]  [<ffffffff81288881>] unmap_vmas+0x61/0xa0
[  265.480172]  [<ffffffff8128f730>] exit_mmap+0xd0/0x170
[  265.480172]  [<ffffffff81138860>] mmput+0x70/0xe0
[  265.480172]  [<ffffffff8113c89d>] exit_mm+0x18d/0x1a0
[  265.480172]  [<ffffffff811ea355>] ? acct_collect+0x175/0x1b0
[  265.480172]  [<ffffffff8113ed0f>] do_exit+0x26f/0x520
[  265.480172]  [<ffffffff8113f069>] do_group_exit+0xa9/0xe0
[  265.480172]  [<ffffffff8113f0b7>] SyS_exit_group+0x17/0x20
[  265.480172]  [<ffffffff845f10d0>] tracesys+0xdd/0xe2
[  265.480172] Code: 0f 0b 66 0f 1f 84 00 00 00 00 00 eb fe 66 0f 1f 44 00 00 48 8b 03 f0 48 81 80 
50 03 00 00 00 fe ff ff 49 8b 45 00 f6 c4 40 75 10 <0f> 0b 66 0f 1f 44 00 00 eb fe 66 0f 1f 44 00 00 
48 8b 03 f0 48
[  265.480172] RIP  [<ffffffff812c7f70>] zap_huge_pmd+0x170/0x1f0
[  265.480172]  RSP <ffff8801cbd3bc78>


Thanks,
Sasha
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