perf_counter, x86: Fix call-chain walking

Fix the ptregs variant when we hit user-mode tasks.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/cpu/perf_counter.c

@@ -1644,7 +1644,9 @@ perf_callchain_user(struct pt_regs *regs, struct perf_callchain_entry *entry)
 	const void __user *fp;
 	int nr = entry->nr;
 
-	regs = (struct pt_regs *)current->thread.sp0 - 1;
+	if (!user_mode(regs))
+		regs = task_pt_regs(current);
+
 	fp   = (void __user *)regs->bp;
 
 	callchain_store(entry, regs->ip);
@@ -1656,7 +1658,7 @@ perf_callchain_user(struct pt_regs *regs, struct perf_callchain_entry *entry)
 		if (!copy_stack_frame(fp, &frame))
 			break;
 
-		if ((unsigned long)fp < user_stack_pointer(regs))
+		if ((unsigned long)fp < regs->sp)
 			break;
 
 		callchain_store(entry, frame.return_address);