This patch fixes the following oops, which could be trigged by build the kernel
with many concurrent threads, under CONFIG_DEBUG_PAGEALLOC.

hpte_insert() might return -1, indicating that the bucket (primary here)
is full. We are not necessarily reporting a BUG in this case. Instead, we could
try repeatedly (try secondary, remove and try again) until we find a slot.

[  543.075675] ------------[ cut here ]------------
[  543.075701] kernel BUG at arch/powerpc/mm/hash_utils_64.c:1239!
[  543.075714] Oops: Exception in kernel mode, sig: 5 [#1]
[  543.075722] PREEMPT SMP NR_CPUS=16 DEBUG_PAGEALLOC NUMA pSeries
[  543.075741] Modules linked in: binfmt_misc ehea
[  543.075759] NIP: c000000000036eb0 LR: c000000000036ea4 CTR: c00000000005a594
[  543.075771] REGS: c0000000a90832c0 TRAP: 0700   Not tainted  (3.8.0-next-20130222)
[  543.075781] MSR: 8000000000029032 <SF,EE,ME,IR,DR,RI>  CR: 22224482  XER: 00000000
[  543.075816] SOFTE: 0
[  543.075823] CFAR: c00000000004c200
[  543.075830] TASK = c0000000e506b750[23934] 'cc1' THREAD: c0000000a9080000 CPU: 1
GPR00: 0000000000000001 c0000000a9083540 c000000000c600a8 ffffffffffffffff
GPR04: 0000000000000050 fffffffffffffffa c0000000a90834e0 00000000004ff594
GPR08: 0000000000000001 0000000000000000 000000009592d4d8 c000000000c86854
GPR12: 0000000000000002 c000000006ead300 0000000000a51000 0000000000000001
GPR16: f000000003354380 ffffffffffffffff ffffffffffffff80 0000000000000000
GPR20: 0000000000000001 c000000000c600a8 0000000000000001 0000000000000001
GPR24: 0000000003354380 c000000000000000 0000000000000000 c000000000b65950
GPR28: 0000002000000000 00000000000cd50e 0000000000bf50d9 c000000000c7c230
[  543.076005] NIP [c000000000036eb0] .kernel_map_pages+0x1e0/0x3f8
[  543.076016] LR [c000000000036ea4] .kernel_map_pages+0x1d4/0x3f8
[  543.076025] Call Trace:
[  543.076033] [c0000000a9083540] [c000000000036ea4] .kernel_map_pages+0x1d4/0x3f8 (unreliable)
[  543.076053] [c0000000a9083640] [c000000000167638] .get_page_from_freelist+0x6cc/0x8dc
[  543.076067] [c0000000a9083800] [c000000000167a48] .__alloc_pages_nodemask+0x200/0x96c
[  543.076082] [c0000000a90839c0] [c0000000001ade44] .alloc_pages_vma+0x160/0x1e4
[  543.076098] [c0000000a9083a80] [c00000000018ce04] .handle_pte_fault+0x1b0/0x7e8
[  543.076113] [c0000000a9083b50] [c00000000018d5a8] .handle_mm_fault+0x16c/0x1a0
[  543.076129] [c0000000a9083c00] [c0000000007bf1dc] .do_page_fault+0x4d0/0x7a4
[  543.076144] [c0000000a9083e30] [c0000000000090e8] handle_page_fault+0x10/0x30
[  543.076155] Instruction dump:
[  543.076163] 7c630038 78631d88 e80a0000 f8410028 7c0903a6 e91f01de e96a0010 e84a0008
[  543.076192] 4e800421 e8410028 7c7107b4 7a200fe0 <0b000000> 7f63db78 48785781 60000000
[  543.076224] ---[ end trace bd5807e8d6ae186b ]---
Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>