x86/locking: Create stack frame in PV unlock

The assembly PV_UNLOCK function is a callable non-leaf function which
doesn't honor CONFIG_FRAME_POINTER, which can result in bad stack
traces.

Create a stack frame when CONFIG_FRAME_POINTER is enabled.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Bernd Petrovitsch <bernd@petrovitsch.priv.at>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chris J Arges <chris.j.arges@canonical.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Pedro Alves <palves@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <Waiman.Long@hpe.com>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/6685a72ddbbd0ad3694337cca0af4b4ea09f5f40.1453405861.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/qspinlock_paravirt.h

@@ -36,8 +36,10 @@ PV_CALLEE_SAVE_REGS_THUNK(__pv_queued_spin_unlock_slowpath);
  */
 asm    (".pushsection .text;"
 	".globl " PV_UNLOCK ";"
+	".type " PV_UNLOCK ", @function;"
 	".align 4,0x90;"
 	PV_UNLOCK ": "
+	FRAME_BEGIN
 	"push  %rdx;"
 	"mov   $0x1,%eax;"
 	"xor   %edx,%edx;"
@@ -45,6 +47,7 @@ asm    (".pushsection .text;"
 	"cmp   $0x1,%al;"
 	"jne   .slowpath;"
 	"pop   %rdx;"
+	FRAME_END
 	"ret;"
 	".slowpath: "
 	"push   %rsi;"
@@ -52,6 +55,7 @@ asm    (".pushsection .text;"
 	"call " PV_UNLOCK_SLOWPATH ";"
 	"pop    %rsi;"
 	"pop    %rdx;"
+	FRAME_END
 	"ret;"
 	".size " PV_UNLOCK ", .-" PV_UNLOCK ";"
 	".popsection");