check: catch general protection fault traces in _check_dmesg

check: catch general protection fault traces in _check_dmesg

While writing a test case for overlayfs I noticed that _check_dmesg()
did not detect general protection fault traces like the following:

[15277.026108] run fstests overlay/002 at 2016-03-21 18:42:27
[15277.933179] general protection fault: 0000 [#11] PREEMPT SMP DEBUG_PAGEALLOC
[15277.935427] Modules linked in: btrfs overlay ppdev crc32c_generic evdev xor raid6_pq psmouse pcspkr sg serio_raw acpi_cpufreq parport_pc parport tpm_tis i2c_piix4
[15277.936011] CPU: 15 PID: 22762 Comm: xfs_io Tainted: G      D         4.5.0-rc6-btrfs-next-26+ #1
[15277.936011] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS by qemu-project.org 04/01/2014
[15277.936011] task: ffff88001f6f1340 ti: ffff88000a3f8000 task.ti: ffff88000a3f8000
[15277.936011] RIP: 0010:[<ffffffffa030b7ab>]  [<ffffffffa030b7ab>] btrfs_sync_file+0x11b/0x3e9 [btrfs]
[15277.936011] RSP: 0018:ffff88000a3fbe40  EFLAGS: 00010286
[15277.936011] RAX: 0000000080000000 RBX: ffff8800b0152c88 RCX: 0000000000000001
[15277.936011] RDX: 0000000000000001 RSI: ffffffff8148fec0 RDI: 00000000ffffffff
[15277.936011] RBP: ffff88000a3fbec0 R08: 0000000000000001 R09: 0000000000000000
[15277.936011] R10: ffff88000a3fbe40 R11: 0000000000000246 R12: 6e756f635f657269
[15277.936011] R13: 0000000000000000 R14: 00000000014655a0 R15: ffff88017dd25e40
[15277.936011] FS:  00007f27f0e1f700(0000) GS:ffff88023ede0000(0000) knlGS:0000000000000000
[15277.936011] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[15277.936011] CR2: 00007f27f0e2f000 CR3: 000000013aadf000 CR4: 00000000000006e0
[15277.936011] Stack:
[15277.936011]  ffffffff8108b5cc ffff88000a3fbec0 0000000000000246 ffff880125abaed0
[15277.936011]  ffff8800b0152d60 8000000000000000 7fffffffffffffff 0000000000000246
[15277.936011]  0000000000000246 ffffffff81074f9b ffffffff8104357c ffff88017dd25e40
[15277.936011] Call Trace:
[15277.936011]  [<ffffffff8108b5cc>] ? arch_local_irq_save+0x9/0xc
[15277.936011]  [<ffffffff81074f9b>] ? ___might_sleep+0xce/0x217
[15277.936011]  [<ffffffff8104357c>] ? __do_page_fault+0x3c0/0x43a
[15277.936011]  [<ffffffff811a2351>] vfs_fsync_range+0x8c/0x9e
[15277.936011]  [<ffffffff811a237f>] vfs_fsync+0x1c/0x1e
[15277.936011]  [<ffffffff811a24d6>] do_fsync+0x31/0x4a
[15277.936011]  [<ffffffff811a2700>] SyS_fsync+0x10/0x14
[15277.936011]  [<ffffffff81493617>] entry_SYSCALL_64_fastpath+0x12/0x6b
[15277.936011] Code: 85 c0 0f 85 e2 02 00 00 48 8b 45 b0 31 f6 4c 29 e8 48 ff c0 48 89 45 a8 48 8d 83 d8 00 00 00 48 89 c7 48 89 45 a0 e8 fc 43 18 e1 <f0> 41 ff 84 24
[15277.936011] RIP  [<ffffffffa030b7ab>] btrfs_sync_file+0x11b/0x3e9 [btrfs]
[15277.936011]  RSP <ffff88000a3fbe40>
[15277.974598] ---[ end trace 721e14960eb939c1 ]---

So teach it to look out for such traces.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>