x86/nmi: Fix use of unallocated cpumask_var_t

Commit "x86/nmi: Perform a safe NMI stack trace on all CPUs" has introduced
a cpumask_var_t variable:

	+static cpumask_var_t printtrace_mask;

But never allocated it before using it, which caused a NULL ptr deref when
trying to print the stack trace:

[ 1110.296154] BUG: unable to handle kernel NULL pointer dereference at           (null)
[ 1110.296169] IP: __memcpy (arch/x86/lib/memcpy_64.S:151)
[ 1110.296178] PGD 4c34b3067 PUD 4c351b067 PMD 0
[ 1110.296186] Oops: 0002 [#1] PREEMPT SMP KASAN
[ 1110.296234] Dumping ftrace buffer:
[ 1110.296330]    (ftrace buffer empty)
[ 1110.296339] Modules linked in:
[ 1110.296345] CPU: 1 PID: 10538 Comm: trinity-c99 Not tainted 3.18.0-rc5-next-20141124-sasha-00058-ge2a8c09-dirty #1499
[ 1110.296348] task: ffff880152650000 ti: ffff8804c3560000 task.ti: ffff8804c3560000
[ 1110.296357] RIP: __memcpy (arch/x86/lib/memcpy_64.S:151)
[ 1110.296360] RSP: 0000:ffff8804c3563870  EFLAGS: 00010246
[ 1110.296363] RAX: 0000000000000000 RBX: ffffe8fff3c4a809 RCX: 0000000000000000
[ 1110.296366] RDX: 0000000000000008 RSI: ffffffff9e254040 RDI: 0000000000000000
[ 1110.296369] RBP: ffff8804c3563908 R08: 0000000000ffffff R09: 0000000000ffffff
[ 1110.296371] R10: 0000000000000000 R11: 0000000000000006 R12: 0000000000000000
[ 1110.296375] R13: 0000000000000000 R14: ffffffff9e254040 R15: ffffe8fff3c4a809
[ 1110.296379] FS:  00007f9e43b0b700(0000) GS:ffff880107e00000(0000) knlGS:0000000000000000
[ 1110.296382] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 1110.296385] CR2: 0000000000000000 CR3: 00000004e4334000 CR4: 00000000000006a0
[ 1110.296400] Stack:
[ 1110.296406]  ffffffff81b1e46c 0000000000000000 ffff880107e03fb8 000000000000000b
[ 1110.296413]  ffff880107dfffc0 ffff880107e03fc0 0000000000000008 ffffffff93f2e9c8
[ 1110.296419]  0000000000000000 ffffda0020fc07f7 0000000000000008 ffff8804c3563901
[ 1110.296420] Call Trace:
[ 1110.296429] ? memcpy (mm/kasan/kasan.c:275)
[ 1110.296437] ? arch_trigger_all_cpu_backtrace (include/linux/bitmap.h:215 include/linux/cpumask.h:506 arch/x86/kernel/apic/hw_nmi.c:76)
[ 1110.296444] arch_trigger_all_cpu_backtrace (include/linux/bitmap.h:215 include/linux/cpumask.h:506 arch/x86/kernel/apic/hw_nmi.c:76)
[ 1110.296451] ? dump_stack (./arch/x86/include/asm/preempt.h:95 lib/dump_stack.c:55)
[ 1110.296458] do_raw_spin_lock (./arch/x86/include/asm/spinlock.h:86 kernel/locking/spinlock_debug.c:130 kernel/locking/spinlock_debug.c:137)
[ 1110.296468] _raw_spin_lock (include/linux/spinlock_api_smp.h:143 kernel/locking/spinlock.c:151)
[ 1110.296474] ? __page_check_address (include/linux/spinlock.h:309 mm/rmap.c:630)
[ 1110.296481] __page_check_address (include/linux/spinlock.h:309 mm/rmap.c:630)
[ 1110.296487] ? preempt_count_sub (kernel/sched/core.c:2615)
[ 1110.296493] try_to_unmap_one (include/linux/rmap.h:202 mm/rmap.c:1146)
[ 1110.296504] ? anon_vma_interval_tree_iter_next (mm/interval_tree.c:72 mm/interval_tree.c:103)
[ 1110.296514] rmap_walk (mm/rmap.c:1653 mm/rmap.c:1725)
[ 1110.296521] ? page_get_anon_vma (include/linux/rcupdate.h:423 include/linux/rcupdate.h:935 mm/rmap.c:435)
[ 1110.296530] try_to_unmap (mm/rmap.c:1545)
[ 1110.296536] ? page_get_anon_vma (mm/rmap.c:437)
[ 1110.296545] ? try_to_unmap_nonlinear (mm/rmap.c:1138)
[ 1110.296551] ? SyS_msync (mm/rmap.c:1501)
[ 1110.296558] ? page_remove_rmap (mm/rmap.c:1409)
[ 1110.296565] ? page_get_anon_vma (mm/rmap.c:448)
[ 1110.296571] ? anon_vma_ctor (mm/rmap.c:1496)
[ 1110.296579] migrate_pages (mm/migrate.c:913 mm/migrate.c:956 mm/migrate.c:1136)
[ 1110.296586] ? _raw_spin_unlock_irq (./arch/x86/include/asm/preempt.h:95 include/linux/spinlock_api_smp.h:169 kernel/locking/spinlock.c:199)
[ 1110.296593] ? buffer_migrate_lock_buffers (mm/migrate.c:1584)
[ 1110.296601] ? handle_mm_fault (mm/memory.c:3163 mm/memory.c:3223 mm/memory.c:3336 mm/memory.c:3365)
[ 1110.296607] migrate_misplaced_page (mm/migrate.c:1738)
[ 1110.296614] handle_mm_fault (mm/memory.c:3170 mm/memory.c:3223 mm/memory.c:3336 mm/memory.c:3365)
[ 1110.296623] __do_page_fault (arch/x86/mm/fault.c:1246)
[ 1110.296630] ? vtime_account_user (kernel/sched/cputime.c:701)
[ 1110.296638] ? get_parent_ip (kernel/sched/core.c:2559)
[ 1110.296646] ? context_tracking_user_exit (kernel/context_tracking.c:144)
[ 1110.296656] trace_do_page_fault (arch/x86/mm/fault.c:1329 include/linux/jump_label.h:114 include/linux/context_tracking_state.h:27 include/linux/context_tracking.h:45 arch/x86/mm/fault.c:1330)
[ 1110.296664] do_async_page_fault (arch/x86/kernel/kvm.c:280)
[ 1110.296670] async_page_fault (arch/x86/kernel/entry_64.S:1285)
[ 1110.296755] Code: 08 4c 8b 54 16 f0 4c 8b 5c 16 f8 4c 89 07 4c 89 4f 08 4c 89 54 17 f0 4c 89 5c 17 f8 c3 90 83 fa 08 72 1b 4c 8b 06 4c 8b 4c 16 f8 <4c> 89 07 4c 89 4c 17 f8 c3 66 2e 0f 1f 84 00 00 00 00 00 83 fa
All code
========
   0:   08 4c 8b 54             or     %cl,0x54(%rbx,%rcx,4)
   4:   16                      (bad)
   5:   f0 4c 8b 5c 16 f8       lock mov -0x8(%rsi,%rdx,1),%r11
   b:   4c 89 07                mov    %r8,(%rdi)
   e:   4c 89 4f 08             mov    %r9,0x8(%rdi)
  12:   4c 89 54 17 f0          mov    %r10,-0x10(%rdi,%rdx,1)
  17:   4c 89 5c 17 f8          mov    %r11,-0x8(%rdi,%rdx,1)
  1c:   c3                      retq
  1d:   90                      nop
  1e:   83 fa 08                cmp    $0x8,%edx
  21:   72 1b                   jb     0x3e
  23:   4c 8b 06                mov    (%rsi),%r8
  26:   4c 8b 4c 16 f8          mov    -0x8(%rsi,%rdx,1),%r9
  2b:*  4c 89 07                mov    %r8,(%rdi)               <-- trapping instruction
  2e:   4c 89 4c 17 f8          mov    %r9,-0x8(%rdi,%rdx,1)
  33:   c3                      retq
  34:   66 2e 0f 1f 84 00 00    nopw   %cs:0x0(%rax,%rax,1)
  3b:   00 00 00
  3e:   83 fa 00                cmp    $0x0,%edx

Code starting with the faulting instruction
===========================================
   0:   4c 89 07                mov    %r8,(%rdi)
   3:   4c 89 4c 17 f8          mov    %r9,-0x8(%rdi,%rdx,1)
   8:   c3                      retq
   9:   66 2e 0f 1f 84 00 00    nopw   %cs:0x0(%rax,%rax,1)
  10:   00 00 00
  13:   83 fa 00                cmp    $0x0,%edx
[ 1110.296760] RIP __memcpy (arch/x86/lib/memcpy_64.S:151)
[ 1110.296763]  RSP <ffff8804c3563870>
[ 1110.296765] CR2: 0000000000000000

Link: http://lkml.kernel.org/r/1416931560-10603-1-git-send-email-sasha.levin@oracle.com



Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>