[BUG] khugepaged crashes on x86_32

[Steven Rostedt <rostedt@goodmis.org>]

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Running ktest.pl overnight using a x86_32 kernel, it crashed several
times at the same location:

[  138.204712] kobject: 'firewire_ohci' (f1f6ae70): fill_kobj_path: path = '/bus/pci/drivers/firewire_ohci'^M
[  143.120618] BUG: unable to handle kernel paging request at fff90004
[  143.121007] IP: [<c050888d>] khugepaged+0x8ee/0xd88
[  143.121007] *pdpt = 0000000001857001 *pde = 00000000023ea067 *pte = 0000000000000000 
[  143.121007] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
[  143.121007] last sysfs file: /sys/devices/pci0000:00/0000:00:1e.0/0000:07:00.0/device
[  143.121007] Modules linked in: firewire_ohci firewire_core e1000 iTCO_wdt i2c_i801 iTCO_vendor_support ata_generic
[  143.121007] 
[  143.121007] Pid: 43, comm: khugepaged Not tainted 2.6.38-rc1-test #1 DG965MQ/        
[  143.167626] kobject: 'fw0' (f26d3ac0): kobject_add_internal: parent: '0000:07:03.0', set: 'devices'
[  143.167876] kobject: 'fw0' (f26d3ac0): kobject_uevent_env
[  143.167891] kobject: 'fw0' (f26d3ac0): fill_kobj_path: path = '/devices/pci0000:00/0000:00:1e.0/0000:07:03.0/fw0'
[  143.167919] firewire_core: created device fw0: GUID 0090270001a9a277, S400
[  143.203012] EIP: 0060:[<c050888d>] EFLAGS: 00010287 CPU: 1
[  143.203012] EIP is at khugepaged+0x8ee/0xd88^M
[  143.203012] EAX: b7600000 EBX: fff91000 ECX: fff90000 EDX: f7356000^M
[  143.203012] ESI: f26327e0 EDI: f26327e0 EBP: f3be3f90 ESP: f3be3ed0
[  143.203012]  DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
[  143.203012] Process khugepaged (pid: 43, ti=f3be2000 task=f3905500 task.ti=f3be2000)
[  143.203012] Stack:
[  143.203012]  f73b2340 f3905500 f3905500 f3905500 00000067 fff91000 00001000 f3905500
[  143.203012]  f3905500 ffa51b4e f3be3f00 7e2da000 00000000 7e2da000 00000000 fff91000
[  143.203012]  f2fb85a8 00000001 00000000 f3905500 00000000 00001000 b7600000 f1891000
[  143.203012] Call Trace:
[  143.203012]  [<c047dc33>] ? autoremove_wake_function+0x0/0x2f
[  143.203012]  [<c0507f9f>] ? khugepaged+0x0/0xd88^M
[  143.203012]  [<c047d8d2>] kthread+0x6d/0x72
[  143.203012]  [<c047d865>] ? kthread+0x0/0x72
[  143.203012]  [<c042c502>] kernel_thread_helper+0x6/0x10
[  143.203012] Code: 7d d8 8b 47 44 8b 00 83 c0 04 e8 91 a3 9c 00 8b 45 d0 8b 55 c4 89 75 b0 89 fe 89 5d ac 89 45 d4 89 55 bc e9 c0 00 00 00 8b 4d dc <8b> 51 04 8b 01 89 d3 09 c3 75 26 8b 45 bc e8 bc 8e f4 ff b9 00 
[  143.203012] EIP: [<c050888d>] khugepaged+0x8ee/0xd88 SS:ESP 0068:f3be3ed0
[  143.203012] CR2: 00000000fff90004
[  143.203012] ---[ end trace 9d821574f573609c ]---
[  145.478023] i2c i2c-9: master_xfer[0] W, addr=0x38, len=2

It's happening in this loop:

static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
				      struct vm_area_struct *vma,
				      unsigned long address,
				      spinlock_t *ptl)
{
	pte_t *_pte;
	for (_pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++) {
		pte_t pteval = *_pte;
		struct page *src_page;


The fault (according to gdb) is at the:

		pte_t pteval = *_pte;

Attached is one of the configs I used to produce this bug.

I hit this bug with both v2.6.38-rc1 and with

HEAD == 12fcdba1b7ae8b25696433f420b775aeb556d89b

Let me know if you need to know anything more.

-- Steve


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