mm: BUG in do_huge_pmd_wp_page

[Sasha Levin]

Hi all,

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

It seems that the code in do_huge_pmd_wp_page() was recently modified in
"thp: do_huge_pmd_wp_page(): handle huge zero page".

Here's the trace:

[  246.244708] BUG: unable to handle kernel paging request at ffff88009c422000
[  246.245743] IP: [<ffffffff81a0a795>] copy_page_rep+0x5/0x10
[  246.250569] PGD 7232067 PUD 7235067 PMD bfefe067 PTE 800000009c422060
[  246.251529] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[  246.252325] Dumping ftrace buffer:
[  246.252791]    (ftrace buffer empty)
[  246.252869] Modules linked in:
[  246.252869] CPU 3
[  246.252869] Pid: 11985, comm: trinity-child12 Tainted: G        W    3.9.0-rc4-next-20130328-sasha-00014-g91a3267 #319
[  246.252869] RIP: 0010:[<ffffffff81a0a795>]  [<ffffffff81a0a795>] copy_page_rep+0x5/0x10
[  246.252869] RSP: 0018:ffff88000015bc40  EFLAGS: 00010286
[  246.252869] RAX: ffff88000015bfd8 RBX: 0000000002710880 RCX: 0000000000000200
[  246.252869] RDX: 0000000000000000 RSI: ffff88009c422000 RDI: ffff88009a422000
[  246.252869] RBP: ffff88000015bc98 R08: 0000000002718000 R09: 0000000000000001
[  246.252869] R10: 0000000000000001 R11: 0000000000000000 R12: ffff880000000000
[  246.252869] R13: ffff88000015bfd8 R14: ffff88000015bfd8 R15: fffffffffff80000
[  246.252869] FS:  00007f53db93f700(0000) GS:ffff8800bba00000(0000) knlGS:0000000000000000
[  246.252869] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  246.252869] CR2: ffff88009c422000 CR3: 0000000000159000 CR4: 00000000000406e0
[  246.252869] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  246.252869] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[  246.252869] Process trinity-child12 (pid: 11985, threadinfo ffff88000015a000, task ffff88009c60b000)
[  246.252869] Stack:
[  246.252869]  ffffffff81234aae ffff88000015bc88 ffffffff81273639 0000000000a00000
[  246.252869]  0000000002718000 ffff8800ab36d050 ffff880000153800 ffffea0002690000
[  246.252869]  0000000000a00000 ffff8800ab36d000 ffffea0002710000 ffff88000015bd48
[  246.252869] Call Trace:
[  246.252869]  [<ffffffff81234aae>] ? copy_user_huge_page+0x1de/0x240
[  246.252869]  [<ffffffff81273639>] ? mem_cgroup_charge_common+0xa9/0xc0
[  246.252869]  [<ffffffff8126b4d7>] do_huge_pmd_wp_page+0x9f7/0xc60
[  246.252869]  [<ffffffff81a0acd9>] ? __const_udelay+0x29/0x30
[  246.252869]  [<ffffffff8123364e>] handle_mm_fault+0x26e/0x650
[  246.252869]  [<ffffffff8117dc1a>] ? __lock_is_held+0x5a/0x80
[  246.252869]  [<ffffffff83db3814>] ? __do_page_fault+0x514/0x5e0
[  246.252869]  [<ffffffff83db3870>] __do_page_fault+0x570/0x5e0
[  246.252869]  [<ffffffff811c6500>] ? rcu_eqs_exit_common+0x60/0x260
[  246.252869]  [<ffffffff811c740e>] ? rcu_eqs_enter_common+0x33e/0x3b0
[  246.252869]  [<ffffffff811c679c>] ? rcu_eqs_exit+0x9c/0xb0
[  246.252869]  [<ffffffff83db3912>] do_page_fault+0x32/0x50
[  246.252869]  [<ffffffff83db2ef0>] do_async_page_fault+0x30/0xc0
[  246.252869]  [<ffffffff83db01e8>] async_page_fault+0x28/0x30
[  246.252869] Code: 90 90 90 90 90 90 9c fa 65 48 3b 06 75 14 65 48 3b 56 08 75 0d 65 48 89 1e 65 48 89 4e 08 9d b0 01 c3 9d 30
c0 c3 b9 00 02 00 00 <f3> 48 a5 c3 0f 1f 80 00 00 00 00 eb ee 66 66 66 90 66 66 66 90
[  246.252869] RIP  [<ffffffff81a0a795>] copy_page_rep+0x5/0x10
[  246.252869]  RSP <ffff88000015bc40>
[  246.252869] CR2: ffff88009c422000
[  246.252869] ---[ end trace 09fbe37b108d5766 ]---

And this is the code:

        if (is_huge_zero_pmd(orig_pmd))
                clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
        else
                copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR); <--- this


Thanks,
Sasha
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