Hi Liviu,

0day kernel testing robot got the below dmesg and the first bad commit is

git://git.kernel.org/pub/scm/linux/kernel/git/robh/linux versatile-mulitplatform
commit d4432d13bf37e7adc09ccf1100e8d22066ab3eb7
Author:     Liviu Dudau <Liviu.Dudau@arm.com>
AuthorDate: Fri Mar 14 15:34:29 2014 +0000
Commit:     Rob Herring <robh@kernel.org>
CommitDate: Wed May 21 15:29:31 2014 -0500

    pci: Create pci_host_bridge before its associated bus in pci_create_root_bus.
        Before commit 7b5436635800 the pci_host_bridge was created before the root bus.
    As that commit has added a needless dependency on the bus for pci_alloc_host_bridge()
    the creation order has been changed for no good reason. Revert the order of
    creation as we are going to depend on the pci_host_bridge structure to retrieve the
    domain number of the root bus.
        Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
    Acked-by: Grant Likely <grant.likely@linaro.org>
    Tested-by: Tanmay Inamdar <tinamdar@apm.com>

+------------------------------------------------------+------------+------------+
|                                                      | 8c64f463cf | d4432d13bf |
+------------------------------------------------------+------------+------------+
| boot_successes                                       | 60         | 0          |
| boot_failures                                        | 0          | 120        |
| BUG:unable_to_handle_kernel_NULL_pointer_dereference | 0          | 120        |
| Oops                                                 | 0          | 120        |
| RIP:pcibios_root_bridge_prepare                      | 0          | 120        |
| Kernel_panic-not_syncing:Fatal_exception             | 0          | 120        |
| backtrace:acpi_bus_scan                              | 0          | 120        |
| backtrace:acpi_scan_init                             | 0          | 120        |
| backtrace:acpi_init                                  | 0          | 120        |
| backtrace:kernel_init_freeable                       | 0          | 120        |
+------------------------------------------------------+------------+------------+


[    0.072806] ACPI: PCI Root Bridge [PCI0] (domain 0000 [bus 00-ff])
[    0.073477] acpi PNP0A03:00: _OSC: OS supports [Segments]
[    0.074073] acpi PNP0A03:00: _OSC failed (AE_NOT_FOUND); disabling ASPM
[    0.075212] BUG: unable to handle kernel NULL pointer dereference at 00000000000000c8
[    0.076055] IP: [<ffffffff812ebc2f>] pcibios_root_bridge_prepare+0xb/0x21
[    0.076772] PGD 0 [    0.077008] Oops: 0000 [#1] [    0.077350] Modules linked in:
[    0.077693] CPU: 0 PID: 1 Comm: swapper Not tainted 3.15.0-rc5-00014-gd4432d1 #7
[    0.078445] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[    0.079029] task: ffff880000052010 ti: ffff880000054000 task.ti: ffff880000054000
[    0.079807] RIP: 0010:[<ffffffff812ebc2f>]  [<ffffffff812ebc2f>] pcibios_root_bridge_prepare+0xb/0x21
[    0.080000] RSP: 0000:ffff880000055c18  EFLAGS: 00010286
[    0.080000] RAX: 0000000000000000 RBX: ffff880000159440 RCX: 0000000000000400
[    0.080000] RDX: 00000000000002b0 RSI: ffff880000165800 RDI: ffff880000165800
[    0.080000] RBP: ffff880000055c18 R08: 00000000000080d0 R09: 0000000000000284
[    0.080000] R10: 0000000000000000 R11: 0000000000000000 R12: ffff880000165800
[    0.080000] R13: 0000000000000000 R14: 0000000000000000 R15: ffff880000165a90
[    0.080000] FS:  0000000000000000(0000) GS:ffffffff81726000(0000) knlGS:0000000000000000
[    0.080000] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[    0.080000] CR2: 00000000000000c8 CR3: 0000000001716000 CR4: 00000000000006b0
[    0.080000] Stack:
[    0.080000]  ffff880000055ca8 ffffffff811c4a4f ffff880000055cd0 ffff880000159470
[    0.080000]  ffffffff81987420 0000000000000020 ffff880000055c80 ffffffff811ac4cc
[    0.080000]  ffff880000055cd0 0000000000000000 0000000000000003 0000000000000003
[    0.080000] Call Trace:
[    0.080000]  [<ffffffff811c4a4f>] pci_create_root_bus+0x70/0x2ed
[    0.080000]  [<ffffffff811ac4cc>] ? __list_add+0x12b/0x146
[    0.080000]  [<ffffffff812ebb9c>] pci_acpi_scan_root+0x280/0x308
[    0.080000]  [<ffffffff811d9403>] acpi_pci_root_add+0x202/0x2dc
[    0.080000]  [<ffffffff811d686a>] acpi_bus_attach+0x8b/0x107
[    0.080000]  [<ffffffff8122a7f5>] ? device_attach+0x7c/0x85
[    0.080000]  [<ffffffff811d68cc>] acpi_bus_attach+0xed/0x107
[    0.080000]  [<ffffffff8122a7f5>] ? device_attach+0x7c/0x85
[    0.080000]  [<ffffffff811d68cc>] acpi_bus_attach+0xed/0x107
[    0.080000]  [<ffffffff811d693c>] acpi_bus_scan+0x56/0x66
[    0.080000]  [<ffffffff81a25051>] ? acpi_sleep_init+0xcc/0xcc
[    0.080000]  [<ffffffff81a25432>] acpi_scan_init+0x54/0x170
[    0.080000]  [<ffffffff81a25051>] ? acpi_sleep_init+0xcc/0xcc
[    0.080000]  [<ffffffff81a25240>] acpi_init+0x1ef/0x24b
[    0.080000]  [<ffffffff8100029b>] do_one_initcall+0x7d/0x13a
[    0.080000]  [<ffffffff8106d36b>] ? parse_args+0x180/0x246
[    0.080000]  [<ffffffff81a02f9d>] kernel_init_freeable+0x1c2/0x24e
[    0.080000]  [<ffffffff81a026ee>] ? do_early_param+0x8a/0x8a
[    0.080000]  [<ffffffff813f7a99>] ? rest_init+0xbd/0xbd
[    0.080000]  [<ffffffff813f7aa2>] kernel_init+0x9/0xd0
[    0.080000]  [<ffffffff8140b9ca>] ret_from_fork+0x7a/0xb0
[    0.080000]  [<ffffffff813f7a99>] ? rest_init+0xbd/0xbd
[    0.080000] Code: 48 c7 c7 27 12 65 81 31 c0 e8 92 b9 f3 ff 4c 89 e8 48 83 c4 28 5b 41 5c 41 5d 41 5e 41 5f 5d c3 48 8b 87 88 02 00 00 55 48 89 e5 <48> 8b 80 c8 00 00 00 5d 48 8b 40 08 48 89 87 d8 01 00 00 31 c0 [    0.080000] RIP  [<ffffffff812ebc2f>] pcibios_root_bridge_prepare+0xb/0x21
[    0.080000]  RSP <ffff880000055c18>
[    0.080000] CR2: 00000000000000c8
[    0.080000] ---[ end trace dbb81a2550228027 ]---
[    0.080000] Kernel panic - not syncing: Fatal exception

git bisect start 7f3a02c2b0f2023dcf5dd98f2dc1524ed7b5b6c9 4b660a7f5c8099d88d1a43d8ae138965112592c7 --
git bisect good 4ed78930ecdc36fcb82d5de534c201593b8e228b  # 23:29     20+      0  Merge 'mvebu/mvebu/soc' into devel-cairo-x86_64-201405222248
git bisect good 52c86ac98d407f77d28b3cfec2a6095eeb796427  # 23:35     20+      0  Merge 'drm-intel/drm-intel-nightly' into devel-cairo-x86_64-201405222248
git bisect  bad ee958e5c81d886293628b6742e8b6d6c2900397c  # 23:49      0-     20  Merge 'robh/versatile-multiplatform' into devel-cairo-x86_64-201405222248
git bisect  bad f5305fb856fa29122994db5031ab781be4b2cb5d  # 00:12      0-     20  pci: Add support for creating a generic host_bridge from device tree
git bisect good 9968eb62ded650fb932a516a2a0ebce133b454fd  # 00:26     20+      0  dt/bindings: add compatible string for versatile osc clock
git bisect good cfb6a908184516c1337c9eb28c76235b42d55a2b  # 00:33     20+      0  pci: Introduce pci_register_io_range() helper function.
git bisect  bad d4432d13bf37e7adc09ccf1100e8d22066ab3eb7  # 00:42      0-     20  pci: Create pci_host_bridge before its associated bus in pci_create_root_bus.
git bisect good 8c64f463cf0babd75b7cc65517bb25e7c70bb5ed  # 00:56     20+      0  pci: OF: Fix the conversion of IO ranges into IO resources.
# first bad commit: [d4432d13bf37e7adc09ccf1100e8d22066ab3eb7] pci: Create pci_host_bridge before its associated bus in pci_create_root_bus.
git bisect good 8c64f463cf0babd75b7cc65517bb25e7c70bb5ed  # 00:58     60+      0  pci: OF: Fix the conversion of IO ranges into IO resources.
git bisect  bad 7f3a02c2b0f2023dcf5dd98f2dc1524ed7b5b6c9  # 00:58      0-     13  0day head guard for 'devel-cairo-x86_64-201405222248'
git bisect good 4b660a7f5c8099d88d1a43d8ae138965112592c7  # 01:01     60+      0  Linux 3.15-rc6
git bisect good 542a6299c6a30caaba4b9a3834fbc3f6f2bf959d  # 01:05     60+      0  Add linux-next specific files for 20140522


This script may reproduce the error.

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

kernel=$1

kvm=(
	qemu-system-x86_64 -cpu kvm64 -enable-kvm 	
	-kernel $kernel
	-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,
Jet