perf: Stop stack frame walking off kernel addresses boundaries

While processing kernel perf callchains, an bad entry can be
considered as a valid stack pointer but not as a kernel address.

In this case, we hang in an endless loop. This can happen in an
x86-32 kernel after processing the last entry in a kernel
stacktrace.

Just stop the stack frame walking after we encounter an invalid
kernel address.

This fixes a hard lockup in x86-32.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1262227945-27014-1-git-send-regression-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/dumpstack.c

@@ -123,13 +123,15 @@ print_context_stack_bp(struct thread_info *tinfo,
 	while (valid_stack_ptr(tinfo, ret_addr, sizeof(*ret_addr), end)) {
 		unsigned long addr = *ret_addr;
 
-		if (__kernel_text_address(addr)) {
-			ops->address(data, addr, 1);
-			frame = frame->next_frame;
-			ret_addr = &frame->return_address;
-			print_ftrace_graph_addr(addr, data, ops, tinfo, graph);
-		}
+		if (!__kernel_text_address(addr))
+			break;
+
+		ops->address(data, addr, 1);
+		frame = frame->next_frame;
+		ret_addr = &frame->return_address;
+		print_ftrace_graph_addr(addr, data, ops, tinfo, graph);
 	}
+
 	return (unsigned long)frame;
 }
 EXPORT_SYMBOL_GPL(print_context_stack_bp);