tracing/function-return-tracer: support for dynamic ftrace on function return tracer

This patch adds the support for dynamic tracing on the function return tracer.
The whole difference with normal dynamic function tracing is that we don't need
to hook on a particular callback. The only pro that we want is to nop or set
dynamically the calls to ftrace_caller (which is ftrace_return_caller here).

Some security checks ensure that we are not trying to launch dynamic tracing for
return tracing while normal function tracing is already running.

An example of trace with getnstimeofday set as a filter:

ktime_get_ts+0x22/0x50 -> getnstimeofday (2283 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1396 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1382 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1825 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1426 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1464 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1524 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1382 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1382 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1434 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1464 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1502 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1404 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1397 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1051 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1314 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1344 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1163 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1390 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1374 ns)

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 141 insertions, 135 deletions

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index f976211..74defe2 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1190,7 +1190,7 @@ ENTRY(mcount)
 	jnz trace
 #ifdef CONFIG_FUNCTION_RET_TRACER
 	cmpl $ftrace_stub, ftrace_function_return
-	jnz trace_return
+	jnz ftrace_return_caller
 #endif
 .globl ftrace_stub
 ftrace_stub:
@@ -1211,9 +1211,15 @@ trace:
 	popl %ecx
 	popl %eax
 	jmp ftrace_stub
+END(mcount)
+#endif /* CONFIG_DYNAMIC_FTRACE */
+#endif /* CONFIG_FUNCTION_TRACER */
 
 #ifdef CONFIG_FUNCTION_RET_TRACER
-trace_return:
+ENTRY(ftrace_return_caller)
+	cmpl $0, function_trace_stop
+	jne ftrace_stub
+
 	pushl %eax
 	pushl %ecx
 	pushl %edx
@@ -1223,7 +1229,8 @@ trace_return:
 	popl %edx
 	popl %ecx
 	popl %eax
-	jmp ftrace_stub
+	ret
+END(ftrace_return_caller)
 
 .globl return_to_handler
 return_to_handler:
@@ -1237,10 +1244,7 @@ return_to_handler:
 	popl %ecx
 	popl %eax
 	ret
-#endif /* CONFIG_FUNCTION_RET_TRACER */
-END(mcount)
-#endif /* CONFIG_DYNAMIC_FTRACE */
-#endif /* CONFIG_FUNCTION_TRACER */
+#endif
 
 .section .rodata,"a"
 #include "syscall_table_32.S"
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index d98b5a8..924153e 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -24,134 +24,6 @@
 #include <asm/nmi.h>
 
 
-
-#ifdef CONFIG_FUNCTION_RET_TRACER
-
-/*
- * These functions are picked from those used on
- * this page for dynamic ftrace. They have been
- * simplified to ignore all traces in NMI context.
- */
-static atomic_t in_nmi;
-
-void ftrace_nmi_enter(void)
-{
-	atomic_inc(&in_nmi);
-}
-
-void ftrace_nmi_exit(void)
-{
-	atomic_dec(&in_nmi);
-}
-
-/* Add a function return address to the trace stack on thread info.*/
-static int push_return_trace(unsigned long ret, unsigned long long time,
-				unsigned long func)
-{
-	int index;
-	struct thread_info *ti = current_thread_info();
-
-	/* The return trace stack is full */
-	if (ti->curr_ret_stack == FTRACE_RET_STACK_SIZE - 1)
-		return -EBUSY;
-
-	index = ++ti->curr_ret_stack;
-	barrier();
-	ti->ret_stack[index].ret = ret;
-	ti->ret_stack[index].func = func;
-	ti->ret_stack[index].calltime = time;
-
-	return 0;
-}
-
-/* Retrieve a function return address to the trace stack on thread info.*/
-static void pop_return_trace(unsigned long *ret, unsigned long long *time,
-				unsigned long *func)
-{
-	int index;
-
-	struct thread_info *ti = current_thread_info();
-	index = ti->curr_ret_stack;
-	*ret = ti->ret_stack[index].ret;
-	*func = ti->ret_stack[index].func;
-	*time = ti->ret_stack[index].calltime;
-	ti->curr_ret_stack--;
-}
-
-/*
- * Send the trace to the ring-buffer.
- * @return the original return address.
- */
-unsigned long ftrace_return_to_handler(void)
-{
-	struct ftrace_retfunc trace;
-	pop_return_trace(&trace.ret, &trace.calltime, &trace.func);
-	trace.rettime = cpu_clock(raw_smp_processor_id());
-	ftrace_function_return(&trace);
-
-	return trace.ret;
-}
-
-/*
- * Hook the return address and push it in the stack of return addrs
- * in current thread info.
- */
-void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
-{
-	unsigned long old;
-	unsigned long long calltime;
-	int faulted;
-	unsigned long return_hooker = (unsigned long)
-				&return_to_handler;
-
-	/* Nmi's are currently unsupported */
-	if (atomic_read(&in_nmi))
-		return;
-
-	/*
-	 * Protect against fault, even if it shouldn't
-	 * happen. This tool is too much intrusive to
-	 * ignore such a protection.
-	 */
-	asm volatile(
-		"1: movl (%[parent_old]), %[old]\n"
-		"2: movl %[return_hooker], (%[parent_replaced])\n"
-		"   movl $0, %[faulted]\n"
-
-		".section .fixup, \"ax\"\n"
-		"3: movl $1, %[faulted]\n"
-		".previous\n"
-
-		".section __ex_table, \"a\"\n"
-		"   .long 1b, 3b\n"
-		"   .long 2b, 3b\n"
-		".previous\n"
-
-		: [parent_replaced] "=r" (parent), [old] "=r" (old),
-		  [faulted] "=r" (faulted)
-		: [parent_old] "0" (parent), [return_hooker] "r" (return_hooker)
-		: "memory"
-	);
-
-	if (WARN_ON(faulted)) {
-		unregister_ftrace_return();
-		return;
-	}
-
-	if (WARN_ON(!__kernel_text_address(old))) {
-		unregister_ftrace_return();
-		*parent = old;
-		return;
-	}
-
-	calltime = cpu_clock(raw_smp_processor_id());
-
-	if (push_return_trace(old, calltime, self_addr) == -EBUSY)
-		*parent = old;
-}
-
-#endif
-
 #ifdef CONFIG_DYNAMIC_FTRACE
 
 union ftrace_code_union {
@@ -450,3 +322,133 @@ int __init ftrace_dyn_arch_init(void *data)
 	return 0;
 }
 #endif
+
+#ifdef CONFIG_FUNCTION_RET_TRACER
+
+#ifndef CONFIG_DYNAMIC_FTRACE
+
+/*
+ * These functions are picked from those used on
+ * this page for dynamic ftrace. They have been
+ * simplified to ignore all traces in NMI context.
+ */
+static atomic_t in_nmi;
+
+void ftrace_nmi_enter(void)
+{
+	atomic_inc(&in_nmi);
+}
+
+void ftrace_nmi_exit(void)
+{
+	atomic_dec(&in_nmi);
+}
+#endif /* !CONFIG_DYNAMIC_FTRACE */
+
+/* Add a function return address to the trace stack on thread info.*/
+static int push_return_trace(unsigned long ret, unsigned long long time,
+				unsigned long func)
+{
+	int index;
+	struct thread_info *ti = current_thread_info();
+
+	/* The return trace stack is full */
+	if (ti->curr_ret_stack == FTRACE_RET_STACK_SIZE - 1)
+		return -EBUSY;
+
+	index = ++ti->curr_ret_stack;
+	barrier();
+	ti->ret_stack[index].ret = ret;
+	ti->ret_stack[index].func = func;
+	ti->ret_stack[index].calltime = time;
+
+	return 0;
+}
+
+/* Retrieve a function return address to the trace stack on thread info.*/
+static void pop_return_trace(unsigned long *ret, unsigned long long *time,
+				unsigned long *func)
+{
+	int index;
+
+	struct thread_info *ti = current_thread_info();
+	index = ti->curr_ret_stack;
+	*ret = ti->ret_stack[index].ret;
+	*func = ti->ret_stack[index].func;
+	*time = ti->ret_stack[index].calltime;
+	ti->curr_ret_stack--;
+}
+
+/*
+ * Send the trace to the ring-buffer.
+ * @return the original return address.
+ */
+unsigned long ftrace_return_to_handler(void)
+{
+	struct ftrace_retfunc trace;
+	pop_return_trace(&trace.ret, &trace.calltime, &trace.func);
+	trace.rettime = cpu_clock(raw_smp_processor_id());
+	ftrace_function_return(&trace);
+
+	return trace.ret;
+}
+
+/*
+ * Hook the return address and push it in the stack of return addrs
+ * in current thread info.
+ */
+void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
+{
+	unsigned long old;
+	unsigned long long calltime;
+	int faulted;
+	unsigned long return_hooker = (unsigned long)
+				&return_to_handler;
+
+	/* Nmi's are currently unsupported */
+	if (atomic_read(&in_nmi))
+		return;
+
+	/*
+	 * Protect against fault, even if it shouldn't
+	 * happen. This tool is too much intrusive to
+	 * ignore such a protection.
+	 */
+	asm volatile(
+		"1: movl (%[parent_old]), %[old]\n"
+		"2: movl %[return_hooker], (%[parent_replaced])\n"
+		"   movl $0, %[faulted]\n"
+
+		".section .fixup, \"ax\"\n"
+		"3: movl $1, %[faulted]\n"
+		".previous\n"
+
+		".section __ex_table, \"a\"\n"
+		"   .long 1b, 3b\n"
+		"   .long 2b, 3b\n"
+		".previous\n"
+
+		: [parent_replaced] "=r" (parent), [old] "=r" (old),
+		  [faulted] "=r" (faulted)
+		: [parent_old] "0" (parent), [return_hooker] "r" (return_hooker)
+		: "memory"
+	);
+
+	if (WARN_ON(faulted)) {
+		unregister_ftrace_return();
+		return;
+	}
+
+	if (WARN_ON(!__kernel_text_address(old))) {
+		unregister_ftrace_return();
+		*parent = old;
+		return;
+	}
+
+	calltime = cpu_clock(raw_smp_processor_id());
+
+	if (push_return_trace(old, calltime, self_addr) == -EBUSY)
+		*parent = old;
+}
+
+#endif /* CONFIG_FUNCTION_RET_TRACER */