tracing: Add trace events for each syscall entry/exit

Layer Frederic's syscall tracer on tracepoints. We create trace events
via hooking into the SYSCALL_DEFINE macros. This allows us to
individually toggle syscall entry and exit points on/off.

Signed-off-by: Jason Baron <jbaron@redhat.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Jiaying Zhang <jiayingz@google.com>
Cc: Martin Bligh <mbligh@google.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Masami Hiramatsu <mhiramat@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

1 files changed, 91 insertions, 92 deletions

diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index 08aed43..c7ae25e 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -1,15 +1,16 @@
 #include <trace/syscall.h>
 #include <linux/kernel.h>
+#include <linux/ftrace.h>
 #include <asm/syscall.h>
 
 #include "trace_output.h"
 #include "trace.h"
 
-/* Keep a counter of the syscall tracing users */
-static int refcount;
-
-/* Prevent from races on thread flags toggling */
 static DEFINE_MUTEX(syscall_trace_lock);
+static int sys_refcount_enter;
+static int sys_refcount_exit;
+static DECLARE_BITMAP(enabled_enter_syscalls, FTRACE_SYSCALL_MAX);
+static DECLARE_BITMAP(enabled_exit_syscalls, FTRACE_SYSCALL_MAX);
 
 /* Option to display the parameters types */
 enum {
@@ -95,53 +96,7 @@ print_syscall_exit(struct trace_iterator *iter, int flags)
 	return TRACE_TYPE_HANDLED;
 }
 
-void start_ftrace_syscalls(void)
-{
-	unsigned long flags;
-	struct task_struct *g, *t;
-
-	mutex_lock(&syscall_trace_lock);
-
-	/* Don't enable the flag on the tasks twice */
-	if (++refcount != 1)
-		goto unlock;
-
-	read_lock_irqsave(&tasklist_lock, flags);
-
-	do_each_thread(g, t) {
-		set_tsk_thread_flag(t, TIF_SYSCALL_FTRACE);
-	} while_each_thread(g, t);
-
-	read_unlock_irqrestore(&tasklist_lock, flags);
-
-unlock:
-	mutex_unlock(&syscall_trace_lock);
-}
-
-void stop_ftrace_syscalls(void)
-{
-	unsigned long flags;
-	struct task_struct *g, *t;
-
-	mutex_lock(&syscall_trace_lock);
-
-	/* There are perhaps still some users */
-	if (--refcount)
-		goto unlock;
-
-	read_lock_irqsave(&tasklist_lock, flags);
-
-	do_each_thread(g, t) {
-		clear_tsk_thread_flag(t, TIF_SYSCALL_FTRACE);
-	} while_each_thread(g, t);
-
-	read_unlock_irqrestore(&tasklist_lock, flags);
-
-unlock:
-	mutex_unlock(&syscall_trace_lock);
-}
-
-void ftrace_syscall_enter(struct pt_regs *regs)
+void ftrace_syscall_enter(struct pt_regs *regs, long id)
 {
 	struct syscall_trace_enter *entry;
 	struct syscall_metadata *sys_data;
@@ -150,6 +105,8 @@ void ftrace_syscall_enter(struct pt_regs *regs)
 	int syscall_nr;
 
 	syscall_nr = syscall_get_nr(current, regs);
+	if (!test_bit(syscall_nr, enabled_enter_syscalls))
+		return;
 
 	sys_data = syscall_nr_to_meta(syscall_nr);
 	if (!sys_data)
@@ -170,7 +127,7 @@ void ftrace_syscall_enter(struct pt_regs *regs)
 	trace_wake_up();
 }
 
-void ftrace_syscall_exit(struct pt_regs *regs)
+void ftrace_syscall_exit(struct pt_regs *regs, long ret)
 {
 	struct syscall_trace_exit *entry;
 	struct syscall_metadata *sys_data;
@@ -178,6 +135,8 @@ void ftrace_syscall_exit(struct pt_regs *regs)
 	int syscall_nr;
 
 	syscall_nr = syscall_get_nr(current, regs);
+	if (!test_bit(syscall_nr, enabled_exit_syscalls))
+		return;
 
 	sys_data = syscall_nr_to_meta(syscall_nr);
 	if (!sys_data)
@@ -196,54 +155,94 @@ void ftrace_syscall_exit(struct pt_regs *regs)
 	trace_wake_up();
 }
 
-static int init_syscall_tracer(struct trace_array *tr)
+int reg_event_syscall_enter(void *ptr)
 {
-	start_ftrace_syscalls();
-
-	return 0;
+	int ret = 0;
+	int num;
+	char *name;
+
+	name = (char *)ptr;
+	num = syscall_name_to_nr(name);
+	if (num < 0 || num >= FTRACE_SYSCALL_MAX)
+		return -ENOSYS;
+	mutex_lock(&syscall_trace_lock);
+	if (!sys_refcount_enter)
+		ret = register_trace_syscall_enter(ftrace_syscall_enter);
+	if (ret) {
+		pr_info("event trace: Could not activate"
+				"syscall entry trace point");
+	} else {
+		set_bit(num, enabled_enter_syscalls);
+		sys_refcount_enter++;
+	}
+	mutex_unlock(&syscall_trace_lock);
+	return ret;
 }
 
-static void reset_syscall_tracer(struct trace_array *tr)
+void unreg_event_syscall_enter(void *ptr)
 {
-	stop_ftrace_syscalls();
-	tracing_reset_online_cpus(tr);
-}
-
-static struct trace_event syscall_enter_event = {
-	.type	 	= TRACE_SYSCALL_ENTER,
-	.trace		= print_syscall_enter,
-};
-
-static struct trace_event syscall_exit_event = {
-	.type	 	= TRACE_SYSCALL_EXIT,
-	.trace		= print_syscall_exit,
-};
+	int num;
+	char *name;
 
-static struct tracer syscall_tracer __read_mostly = {
-	.name	     	= "syscall",
-	.init		= init_syscall_tracer,
-	.reset		= reset_syscall_tracer,
-	.flags		= &syscalls_flags,
-};
+	name = (char *)ptr;
+	num = syscall_name_to_nr(name);
+	if (num < 0 || num >= FTRACE_SYSCALL_MAX)
+		return;
+	mutex_lock(&syscall_trace_lock);
+	sys_refcount_enter--;
+	clear_bit(num, enabled_enter_syscalls);
+	if (!sys_refcount_enter)
+		unregister_trace_syscall_enter(ftrace_syscall_enter);
+	mutex_unlock(&syscall_trace_lock);
+}
 
-__init int register_ftrace_syscalls(void)
+int reg_event_syscall_exit(void *ptr)
 {
-	int ret;
-
-	ret = register_ftrace_event(&syscall_enter_event);
-	if (!ret) {
-		printk(KERN_WARNING "event %d failed to register\n",
-		       syscall_enter_event.type);
-		WARN_ON_ONCE(1);
+	int ret = 0;
+	int num;
+	char *name;
+
+	name = (char *)ptr;
+	num = syscall_name_to_nr(name);
+	if (num < 0 || num >= FTRACE_SYSCALL_MAX)
+		return -ENOSYS;
+	mutex_lock(&syscall_trace_lock);
+	if (!sys_refcount_exit)
+		ret = register_trace_syscall_exit(ftrace_syscall_exit);
+	if (ret) {
+		pr_info("event trace: Could not activate"
+				"syscall exit trace point");
+	} else {
+		set_bit(num, enabled_exit_syscalls);
+		sys_refcount_exit++;
 	}
+	mutex_unlock(&syscall_trace_lock);
+	return ret;
+}
 
-	ret = register_ftrace_event(&syscall_exit_event);
-	if (!ret) {
-		printk(KERN_WARNING "event %d failed to register\n",
-		       syscall_exit_event.type);
-		WARN_ON_ONCE(1);
-	}
+void unreg_event_syscall_exit(void *ptr)
+{
+	int num;
+	char *name;
 
-	return register_tracer(&syscall_tracer);
+	name = (char *)ptr;
+	num = syscall_name_to_nr(name);
+	if (num < 0 || num >= FTRACE_SYSCALL_MAX)
+		return;
+	mutex_lock(&syscall_trace_lock);
+	sys_refcount_exit--;
+	clear_bit(num, enabled_exit_syscalls);
+	if (!sys_refcount_exit)
+		unregister_trace_syscall_exit(ftrace_syscall_exit);
+	mutex_unlock(&syscall_trace_lock);
 }
-device_initcall(register_ftrace_syscalls);
+
+struct trace_event event_syscall_enter = {
+	.trace			= print_syscall_enter,
+	.type			= TRACE_SYSCALL_ENTER
+};
+
+struct trace_event event_syscall_exit = {
+	.trace			= print_syscall_exit,
+	.type			= TRACE_SYSCALL_EXIT
+};