6 files changed, 86 insertions, 10 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6f20718d3156..d09e812c6223 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -29,6 +29,7 @@ config X86
         select HAVE_FTRACE_MCOUNT_RECORD
         select HAVE_DYNAMIC_FTRACE
         select HAVE_FUNCTION_TRACER
+        select HAVE_FUNCTION_TRACE_MCOUNT_TEST
         select HAVE_KVM if ((X86_32 && !X86_VOYAGER && !X86_VISWS && !X86_NUMAQ) || X86_64)
         select HAVE_ARCH_KGDB if !X86_VOYAGER
         select HAVE_ARCH_TRACEHOOK
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 28b597ef9ca1..9134de814c97 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1157,6 +1157,9 @@ ENTRY(mcount)
 END(mcount)
 
 ENTRY(ftrace_caller)
+        cmpl $0, function_trace_stop
+        jne  ftrace_stub
+
         pushl %eax
         pushl %ecx
         pushl %edx
@@ -1180,6 +1183,9 @@ END(ftrace_caller)
 #else /* ! CONFIG_DYNAMIC_FTRACE */
 
 ENTRY(mcount)
+        cmpl $0, function_trace_stop
+        jne  ftrace_stub
+
         cmpl $ftrace_stub, ftrace_trace_function
         jnz trace
 .globl ftrace_stub
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index b86f332c96a6..08aa6b10933c 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -68,6 +68,8 @@ ENTRY(mcount)
 END(mcount)
 
 ENTRY(ftrace_caller)
+        cmpl $0, function_trace_stop
+        jne  ftrace_stub
 
         /* taken from glibc */
         subq $0x38, %rsp
@@ -103,6 +105,9 @@ END(ftrace_caller)
 
 #else /* ! CONFIG_DYNAMIC_FTRACE */
 ENTRY(mcount)
+        cmpl $0, function_trace_stop
+        jne  ftrace_stub
+
         cmpq $ftrace_stub, ftrace_trace_function
         jnz trace
 .globl ftrace_stub
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 4642959e5bda..794ab907dbfe 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -23,6 +23,34 @@ struct ftrace_ops {
         struct ftrace_ops *next;
 };
 
+extern int function_trace_stop;
+
+/**
+ * ftrace_stop - stop function tracer.
+ *
+ * A quick way to stop the function tracer. Note this an on off switch,
+ * it is not something that is recursive like preempt_disable.
+ * This does not disable the calling of mcount, it only stops the
+ * calling of functions from mcount.
+ */
+static inline void ftrace_stop(void)
+{
+        function_trace_stop = 1;
+}
+
+/**
+ * ftrace_start - start the function tracer.
+ *
+ * This function is the inverse of ftrace_stop. This does not enable
+ * the function tracing if the function tracer is disabled. This only
+ * sets the function tracer flag to continue calling the functions
+ * from mcount.
+ */
+static inline void ftrace_start(void)
+{
+        function_trace_stop = 0;
+}
+
 /*
  * The ftrace_ops must be a static and should also
  * be read_mostly.  These functions do modify read_mostly variables
@@ -41,6 +69,8 @@ extern void ftrace_stub(unsigned long a0, unsigned long a1);
 # define unregister_ftrace_function(ops) do { } while (0)
 # define clear_ftrace_function(ops) do { } while (0)
 static inline void ftrace_kill(void) { }
+static inline void ftrace_stop(void) { }
+static inline void ftrace_start(void) { }
 #endif /* CONFIG_FUNCTION_TRACER */
 
 #ifdef CONFIG_DYNAMIC_FTRACE
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 33dbefd471e8..fc4febc3334a 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -9,6 +9,13 @@ config NOP_TRACER
 config HAVE_FUNCTION_TRACER
         bool
 
+config HAVE_FUNCTION_TRACE_MCOUNT_TEST
+        bool
+        help
+         This gets selected when the arch tests the function_trace_stop
+         variable at the mcount call site. Otherwise, this variable
+         is tested by the called function.
+
 config HAVE_DYNAMIC_FTRACE
         bool
 
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 4a39d24568c8..896c71f0f4c4 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -47,6 +47,9 @@
 int ftrace_enabled __read_mostly;
 static int last_ftrace_enabled;
 
+/* Quick disabling of function tracer. */
+int function_trace_stop;
+
 /*
  * ftrace_disabled is set when an anomaly is discovered.
  * ftrace_disabled is much stronger than ftrace_enabled.
@@ -63,6 +66,7 @@ static struct ftrace_ops ftrace_list_end __read_mostly =
 
 static struct ftrace_ops *ftrace_list __read_mostly = &ftrace_list_end;
 ftrace_func_t ftrace_trace_function __read_mostly = ftrace_stub;
+ftrace_func_t __ftrace_trace_function __read_mostly = ftrace_stub;
 
 static void ftrace_list_func(unsigned long ip, unsigned long parent_ip)
 {
@@ -88,8 +92,23 @@ static void ftrace_list_func(unsigned long ip, unsigned long parent_ip)
 void clear_ftrace_function(void)
 {
         ftrace_trace_function = ftrace_stub;
+        __ftrace_trace_function = ftrace_stub;
 }
 
+#ifndef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST
+/*
+ * For those archs that do not test ftrace_trace_stop in their
+ * mcount call site, we need to do it from C.
+ */
+static void ftrace_test_stop_func(unsigned long ip, unsigned long parent_ip)
+{
+        if (function_trace_stop)
+                return;
+
+        __ftrace_trace_function(ip, parent_ip);
+}
+#endif
+
 static int __register_ftrace_function(struct ftrace_ops *ops)
 {
         /* should not be called from interrupt context */
@@ -110,10 +129,18 @@ static int __register_ftrace_function(struct ftrace_ops *ops)
                  * For one func, simply call it directly.
                  * For more than one func, call the chain.
                  */
+#ifdef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST
                 if (ops->next == &ftrace_list_end)
                         ftrace_trace_function = ops->func;
                 else
                         ftrace_trace_function = ftrace_list_func;
+#else
+                if (ops->next == &ftrace_list_end)
+                        __ftrace_trace_function = ops->func;
+                else
+                        __ftrace_trace_function = ftrace_list_func;
+                ftrace_trace_function = ftrace_test_stop_func;
+#endif
         }
 
         spin_unlock(&ftrace_lock);
@@ -526,7 +553,7 @@ static void ftrace_run_update_code(int command)
 }
 
 static ftrace_func_t saved_ftrace_func;
-static int ftrace_start;
+static int ftrace_start_up;
 static DEFINE_MUTEX(ftrace_start_lock);
 
 static void ftrace_startup(void)
@@ -537,8 +564,8 @@ static void ftrace_startup(void)
                 return;
 
         mutex_lock(&ftrace_start_lock);
-        ftrace_start++;
-        if (ftrace_start == 1)
+        ftrace_start_up++;
+        if (ftrace_start_up == 1)
                 command |= FTRACE_ENABLE_CALLS;
 
         if (saved_ftrace_func != ftrace_trace_function) {
@@ -562,8 +589,8 @@ static void ftrace_shutdown(void)
                 return;
 
         mutex_lock(&ftrace_start_lock);
-        ftrace_start--;
-        if (!ftrace_start)
+        ftrace_start_up--;
+        if (!ftrace_start_up)
                 command |= FTRACE_DISABLE_CALLS;
 
         if (saved_ftrace_func != ftrace_trace_function) {
@@ -589,8 +616,8 @@ static void ftrace_startup_sysctl(void)
         mutex_lock(&ftrace_start_lock);
         /* Force update next time */
         saved_ftrace_func = NULL;
-        /* ftrace_start is true if we want ftrace running */
-        if (ftrace_start)
+        /* ftrace_start_up is true if we want ftrace running */
+        if (ftrace_start_up)
                 command |= FTRACE_ENABLE_CALLS;
 
         ftrace_run_update_code(command);
@@ -605,8 +632,8 @@ static void ftrace_shutdown_sysctl(void)
                 return;
 
         mutex_lock(&ftrace_start_lock);
-        /* ftrace_start is true if ftrace is running */
-        if (ftrace_start)
+        /* ftrace_start_up is true if ftrace is running */
+        if (ftrace_start_up)
                 command |= FTRACE_DISABLE_CALLS;
 
         ftrace_run_update_code(command);
@@ -1186,7 +1213,7 @@ ftrace_regex_release(struct inode *inode, struct file *file, int enable)
 
         mutex_lock(&ftrace_sysctl_lock);
         mutex_lock(&ftrace_start_lock);
-        if (iter->filtered && ftrace_start && ftrace_enabled)
+        if (iter->filtered && ftrace_start_up && ftrace_enabled)
                 ftrace_run_update_code(FTRACE_ENABLE_CALLS);
         mutex_unlock(&ftrace_start_lock);
         mutex_unlock(&ftrace_sysctl_lock);