FYI, here is a very old warning, too old to be bisected.

[    5.282127] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, supports DPO and FUA
[    5.286079] SBC-GXx flash: IO:0x258-0x259 MEM:0xdc000-0xdffff
[    5.288723] ------------[ cut here ]------------
[    5.289649] kernel BUG at include/linux/mtd/map.h:148!
[    5.289649] invalid opcode: 0000 [#1] PREEMPT DEBUG_PAGEALLOC
[    5.289649] CPU: 0 PID: 1 Comm: swapper Not tainted 3.14.0-rc8-wl-03045-gdf16ea4 #6
[    5.289649] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[    5.289649] task: d1c48000 ti: d1c36000 task.ti: d1c36000
[    5.289649] EIP: 0060:[<c17982d8>] EFLAGS: 00010296 CPU: 0
[    5.289649] EIP is at mtd_do_chip_probe+0x15/0x17
[    5.289649] EAX: 00000000 EBX: c242bf28 ECX: 00000000 EDX: d1c37e88
[    5.289649] ESI: c2275f71 EDI: d1c37ec4 EBP: d1c37ec8 ESP: d1c37e88
[    5.289649]  DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068
[    5.289649] CR0: 8005003b CR2: 00000000 CR3: 02556000 CR4: 000006f0
[    5.289649] Stack:
[    5.289649]  00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[    5.289649]  00000000 00000000 00000000 00000000 00000000 00000000 00000000 c242c500
[    5.289649]  d1c37ed0 c1794d3e d1c37ee4 c1794cf5 00000000 c24f0561 00000564 d1c37f04
[    5.289649] Call Trace:
[    5.289649]  [<c1794d3e>] cfi_probe+0xd/0xf
[    5.289649]  [<c1794cf5>] do_map_probe+0x50/0x66
[    5.289649]  [<c24f0561>] ? init_ck804xrom+0x37d/0x37d
[    5.289649]  [<c24f0649>] init_sbc_gxx+0xe8/0x123
[    5.289649]  [<c24b8b54>] do_one_initcall+0x80/0x107
[    5.289649]  [<c13e5049>] ? strlen+0xf/0x19
[    5.289649]  [<c24b8500>] ? repair_env_string+0xa/0x51
[    5.289649]  [<c1049aef>] ? parse_args+0x1bd/0x308
[    5.289649]  [<c1056a24>] ? __wake_up+0x3a/0x42
[    5.289649]  [<c24b8cd0>] kernel_init_freeable+0xf5/0x18c
[    5.289649]  [<c24b84f6>] ? do_early_param+0x78/0x78
[    5.289649]  [<c1e80009>] kernel_init+0xb/0xc2
[    5.289649]  [<c1051d85>] ? schedule_tail+0x12/0x3a
[    5.289649]  [<c1e93e3b>] ret_from_kernel_thread+0x1b/0x30
[    5.289649]  [<c1e7fffe>] ? rest_init+0x6e/0x6e
[    5.289649] Code: e9 1e fd ff ff c7 04 24 44 8e 30 c2 e8 df df 6e 00 e9 28 fb ff ff 55 31 c0 89 e5 b9 0f 00 00 00 8d 55 c0 57 89 d7 83 ec 3c f3 ab <0f> 0b 55 ba 90 c1 42 c2 89 e5 e8 dc ff ff ff 5d c3 55 89 e5 57
[    5.289649] EIP: [<c17982d8>] mtd_do_chip_probe+0x15/0x17 SS:ESP 0068:d1c37e88
[    5.425765] ---[ end trace ad16f43410cd0373 ]---
[    5.428287] swapper (1) used greatest stack depth: 5800 bytes left

git bisect  bad df16ea4de143a63d0f598003bde671cc277390e0  # 16:57      0-     25  0day head guard for 'devel-hourly-2014032612'
git bisect  bad b098d6726bbfb94c06d6e1097466187afddae61f  # 16:58      0-     20  Linux 3.14-rc8
git bisect  bad d8ec26d7f8287f5788a494f56e8814210f0e64be  # 16:58      0-     20  Linux 3.13
git bisect  bad 5e01dc7b26d9f24f39abace5da98ccbd6a5ceb52  # 16:58      0-     20  Linux 3.12
git bisect  bad 6e4664525b1db28f8c4e1130957f70a94c19213e  # 16:58      0-     20  Linux 3.11
git bisect  bad 8bb495e3f02401ee6f76d1b1d77f3ac9f079e376  # 16:58      0-     20  Linux 3.10
git bisect  bad c1be5a5b1b355d40e6cf79cc979eb66dafa24ad1  # 16:58      0-     20  Linux 3.9
git bisect  bad 19f949f52599ba7c3f67a5897ac6be14bfcb1200  # 16:58      0-     20  Linux 3.8
git bisect  bad 29594404d7fe73cd80eaa4ee8c43dcc53970c60e  # 16:59      0-     20  Linux 3.7
git bisect  bad a0d271cbfed1dd50278c6b06bead3d00ba0a88f9  # 16:59      0-     20  Linux 3.6
git bisect  bad 28a33cbc24e4256c143dce96c7d93bf423229f92  # 16:59      0-     20  Linux 3.5
git bisect  bad 76e10d158efb6d4516018846f60c2ab5501900bc  # 16:59      0-     20  Linux 3.4
git bisect  bad c16fa4f2ad19908a47c63d8fa436a1178438c7e7  # 16:59      0-     40  Linux 3.3
git bisect  bad 805a6af8dba5dfdd35ec35dc52ec0122400b2610  # 16:59      0-     20  Linux 3.2
git bisect  bad c3b92c8787367a8bb53d57d9789b558f1295cc96  # 16:59      0-     20  Linux 3.1
git bisect  bad 02f8c6aee8df3cdc935e9bdd4f2d020306035dbe  # 16:59      0-     20  Linux 3.0


This script may reproduce the error.

-----------------------------------------------------------------------------
#!/bin/bash

kernel=$1
initrd=quantal-core-i386.cgz

wget --no-clobber https://github.com/fengguang/reproduce-kernel-bug/blob/master/initrd/$initrd

kvm=(
	qemu-system-x86_64 -cpu kvm64 -enable-kvm
	-kernel $kernel
	-initrd $initrd
	-smp 2
	-m 256M
	-net nic,vlan=0,macaddr=00:00:00:00:00:00,model=virtio
	-net user,vlan=0
	-net nic,vlan=1,model=e1000
	-net user,vlan=1
	-boot order=nc
	-no-reboot
	-watchdog i6300esb
	-serial stdio
	-display none
	-monitor null
)

append=(
	debug
	sched_debug
	apic=debug
	ignore_loglevel
	sysrq_always_enabled
	panic=10
	prompt_ramdisk=0
	earlyprintk=ttyS0,115200
	console=ttyS0,115200
	console=tty0
	vga=normal
	root=/dev/ram0
	rw
)

"${kvm[@]}" --append "${append[*]}"
-----------------------------------------------------------------------------

Thanks,
Fengguang