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Subject[PATCH 1/3] ftrace: add quick function trace stop
Impact: quick start and stop of function tracer

This patch adds a way to disable the function tracer quickly without
the need to run kstop_machine. It adds a new variable called
function_trace_stop which will stop the calls to functions from mcount
when set. This is just an on/off switch and does not handle recursion
like preempt_disable().

It's main purpose is to help other tracers/debuggers start and stop tracing
fuctions without the need to call kstop_machine.

The config option HAVE_FUNCTION_TRACE_MCOUNT_TEST is added for archs
that implement the testing of the function_trace_stop in the mcount
arch dependent code. Otherwise, the test is done in the C code.

x86 is the only arch at the moment that supports this.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
---
arch/x86/Kconfig | 1 +
arch/x86/kernel/entry_32.S | 6 +++++
arch/x86/kernel/entry_64.S | 5 ++++
include/linux/ftrace.h | 30 ++++++++++++++++++++++++++++
kernel/trace/Kconfig | 7 ++++++
kernel/trace/ftrace.c | 47 ++++++++++++++++++++++++++++++++++---------
6 files changed, 86 insertions(+), 10 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index b47b3a6..d5dbfe0 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 28b597e..9134de8 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 ddeeb10..983d85a 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 0ead706..6eb966d 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 33dbefd..fc4febc 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 4a39d24..896c71f 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);
--
1.5.6.5
--


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