Bug fix: Do not free page split from hugepage one by one.

Bug fix: Do not free page split from hugepage one by one.

When we split a larger page into smaller ones, we should not free them one
by one because only the _count of the first page struct makes sense.
Otherwise, the kernel will panic.

So fulfill the unused small pages with 0xFD, and when the whole larger
page is fulfilled with 0xFD, free the whole larger page.

The call trace is like the following:

[ 1052.819430] ------------[ cut here ]------------
[ 1052.874575] kernel BUG at include/linux/mm.h:278!
[ 1052.930754] invalid opcode: 0000 [#1] SMP
[ 1052.979888] Modules linked in: ip6table_filter ip6_tables ebtable_nat ebtables nf_conntrack_ipv4 nf_defrag_ipv4 xt_state nf_conntrack ipt_REJECT xt_CHECKSUM iptable_mangle iptable_filter ip_tables bridge stp llc sunrpc binfmt_misc dm_mirror dm_region_hash dm_log dm_mod vhost_net macvtap macvlan tun uinput iTCO_wdt iTCO_vendor_support coretemp kvm_intel kvm crc32c_intel microcode pcspkr sg i2c_i801 i2c_core lpc_ich mfd_core ioatdma e1000e i7core_edac edac_core igb dca ptp pps_core sd_mod crc_t10dif megaraid_sas mptsas mptscsih mptbase scsi_transport_sas scsi_mod
[ 1053.580111] CPU 0
[ 1053.602026] Pid: 4, comm: kworker/0:0 Tainted: G        W    3.8.0-rc2-memory-hotremove+ #3 FUJITSU-SV PRIMEQUEST 1800E/SB
[ 1053.736188] RIP: 0010:[<ffffffff81175bd7>]  [<ffffffff81175bd7>] __free_pages+0x37/0x50
[ 1053.831952] RSP: 0018:ffff8807bdcb37f8  EFLAGS: 00010246
[ 1053.895403] RAX: 0000000000000000 RBX: ffff88077c401000 RCX: 000000000000002c
[ 1053.980660] RDX: ffff8807fffd7000 RSI: 0000000000000000 RDI: ffffea001df10040
[ 1054.065917] RBP: ffff8807bdcb37f8 R08: 0000000000000000 R09: 0000000000000000
[ 1054.151178] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[ 1054.236433] R13: ffffea0040008000 R14: ffffea0040002000 R15: 00003ffffffff000
[ 1054.321691] FS:  0000000000000000(0000) GS:ffff8807c1a00000(0000) knlGS:0000000000000000
[ 1054.418372] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 1054.487015] CR2: 00007fbc137ad000 CR3: 0000000001c0c000 CR4: 00000000000007f0
[ 1054.572272] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1054.657533] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[ 1054.742797] Process kworker/0:0 (pid: 4, threadinfo ffff8807bdcb2000, task ffff8807bde18000)
[ 1054.843628] Stack:
[ 1054.867622]  ffff8807bdcb3818 ffffffff81175ccf 000000077c401000 ffff880796349008
[ 1054.956421]  ffff8807bdcb3848 ffffffff816a16e2 ffffea0040001000 ffff880796349008
[ 1055.045227]  ffffea0040008000 ffffea0040002000 ffff8807bdcb38b8 ffffffff816a181c
[ 1055.134033] Call Trace:
[ 1055.163230]  [<ffffffff81175ccf>] free_pages+0x5f/0x70
[ 1055.224611]  [<ffffffff816a16e2>] free_pagetable+0x7f/0xee
[ 1055.290147]  [<ffffffff816a181c>] remove_pte_table+0xcb/0x1cd
[ 1055.358806]  [<ffffffff81055bd0>] ? leave_mm+0x50/0x50
[ 1055.420187]  [<ffffffff810df55d>] ? trace_hardirqs_on+0xd/0x10
[ 1055.489882]  [<ffffffff816a1f8b>] remove_pmd_table+0x191/0x253
[ 1055.559576]  [<ffffffff816a261e>] remove_pud_table+0x194/0x24d
[ 1055.629270]  [<ffffffff811bbc3f>] ? sparse_remove_one_section+0x2f/0x150
[ 1055.709348]  [<ffffffff816a278c>] remove_pagetable+0xb5/0x17c
[ 1055.778002]  [<ffffffff81692f28>] vmemmap_free+0x18/0x20
[ 1055.841465]  [<ffffffff811bbd15>] sparse_remove_one_section+0x105/0x150
[ 1055.920508]  [<ffffffff811c953c>] __remove_pages+0xec/0x110
[ 1055.987087]  [<ffffffff81692fa7>] arch_remove_memory+0x77/0xc0
[ 1056.056781]  [<ffffffff81694138>] remove_memory+0xb8/0xf0
[ 1056.121284]  [<ffffffff814040aa>] acpi_memory_device_remove+0x76/0xbc
[ 1056.198244]  [<ffffffff813c1e50>] acpi_device_remove+0x90/0xb2
[ 1056.267941]  [<ffffffff8146bf3c>] __device_release_driver+0x7c/0xf0
[ 1056.342824]  [<ffffffff8146c0bf>] device_release_driver+0x2f/0x50
[ 1056.415635]  [<ffffffff813c3142>] acpi_bus_remove+0x32/0x6d
[ 1056.482215]  [<ffffffff813c320e>] acpi_bus_trim+0x91/0x102
[ 1056.547755]  [<ffffffff813c3307>] acpi_bus_hot_remove_device+0x88/0x180
[ 1056.626794]  [<ffffffff813be152>] acpi_os_execute_deferred+0x27/0x34
[ 1056.702717]  [<ffffffff81091c5e>] process_one_work+0x20e/0x5c0
[ 1056.772411]  [<ffffffff81091bef>] ? process_one_work+0x19f/0x5c0
[ 1056.844184]  [<ffffffff813be12b>] ? acpi_os_wait_events_complete+0x23/0x23
[ 1056.926337]  [<ffffffff81093cfe>] worker_thread+0x12e/0x370
[ 1056.992908]  [<ffffffff81093bd0>] ? manage_workers+0x180/0x180
[ 1057.062602]  [<ffffffff81099e3e>] kthread+0xee/0x100
[ 1057.121913]  [<ffffffff810e10b9>] ? __lock_release+0x129/0x190
[ 1057.191609]  [<ffffffff81099d50>] ? __init_kthread_worker+0x70/0x70
[ 1057.266494]  [<ffffffff816b33ac>] ret_from_fork+0x7c/0xb0
[ 1057.330992]  [<ffffffff81099d50>] ? __init_kthread_worker+0x70/0x70
[ 1057.405863] Code: 85 c0 74 27 f0 ff 4f 1c 0f 94 c0 84 c0 74 0a 85 f6 74 11 90 e8 bb e3 ff ff c9 c3 66 0f 1f 84 00 00 00 00 00 e8 1b fe ff ff c9 c3 <0f> 0b 0f 1f 80 00 00 00 00 eb f7 66 66 66 66 66 2e 0f 1f 84 00
[ 1057.638271] RIP  [<ffffffff81175bd7>] __free_pages+0x37/0x50
[ 1057.705994]  RSP <ffff8807bdcb37f8>
[ 1057.747882] ---[ end trace 0f90e1e054d174f9 ]---
[ 1057.803158] Kernel panic - not syncing: Fatal exception

Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Jiang Liu <jiang.liu@huawei.com>
Cc: Jianguo Wu <wujianguo@huawei.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>