ftrace: add ability to only trace swapper tasks

Impact: new feature

This patch lets the swapper tasks of all CPUS be filtered by the
set_ftrace_pid file.

If '0' is echoed into this file, then all the idle tasks (aka swapper)
is flagged to be traced.  This affects all CPU idle tasks.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 10b1d7c1b1ddb316b173763d4212d3f4cf31d973..eb57dc1ea097b2fc913afc83386a2c92c01698a6 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -49,6 +49,7 @@ static int last_ftrace_enabled;
 
 /* set when tracing only a pid */
 struct pid *ftrace_pid_trace;
+static struct pid * const ftrace_swapper_pid = (struct pid *)1;
 
 /* Quick disabling of function tracer. */
 int function_trace_stop;
@@ -1678,7 +1679,9 @@ ftrace_pid_read(struct file *file, char __user *ubuf,
        char buf[64];
        int r;
 
-       if (ftrace_pid_trace)
+       if (ftrace_pid_trace == ftrace_swapper_pid)
+               r = sprintf(buf, "swapper tasks\n");
+       else if (ftrace_pid_trace)
                r = sprintf(buf, "%u\n", pid_nr(ftrace_pid_trace));
        else
                r = sprintf(buf, "no pid\n");
@@ -1686,19 +1689,43 @@ ftrace_pid_read(struct file *file, char __user *ubuf,
        return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
 }
 
-static void clear_ftrace_pid_task(struct pid **pid)
+static void clear_ftrace_swapper(void)
 {
        struct task_struct *p;
+       int cpu;
 
-       do_each_pid_task(*pid, PIDTYPE_PID, p) {
+       get_online_cpus();
+       for_each_online_cpu(cpu) {
+               p = idle_task(cpu);
                clear_tsk_trace_trace(p);
-       } while_each_pid_task(*pid, PIDTYPE_PID, p);
-       put_pid(*pid);
+       }
+       put_online_cpus();
+}
 
-       *pid = NULL;
+static void set_ftrace_swapper(void)
+{
+       struct task_struct *p;
+       int cpu;
+
+       get_online_cpus();
+       for_each_online_cpu(cpu) {
+               p = idle_task(cpu);
+               set_tsk_trace_trace(p);
+       }
+       put_online_cpus();
 }
 
-static void set_ftrace_pid_task(struct pid *pid)
+static void clear_ftrace_pid(struct pid *pid)
+{
+       struct task_struct *p;
+
+       do_each_pid_task(pid, PIDTYPE_PID, p) {
+               clear_tsk_trace_trace(p);
+       } while_each_pid_task(pid, PIDTYPE_PID, p);
+       put_pid(pid);
+}
+
+static void set_ftrace_pid(struct pid *pid)
 {
        struct task_struct *p;
 
@@ -1707,6 +1734,24 @@ static void set_ftrace_pid_task(struct pid *pid)
        } while_each_pid_task(pid, PIDTYPE_PID, p);
 }
 
+static void clear_ftrace_pid_task(struct pid **pid)
+{
+       if (*pid == ftrace_swapper_pid)
+               clear_ftrace_swapper();
+       else
+               clear_ftrace_pid(*pid);
+
+       *pid = NULL;
+}
+
+static void set_ftrace_pid_task(struct pid *pid)
+{
+       if (pid == ftrace_swapper_pid)
+               set_ftrace_swapper();
+       else
+               set_ftrace_pid(pid);
+}
+
 static ssize_t
 ftrace_pid_write(struct file *filp, const char __user *ubuf,
                   size_t cnt, loff_t *ppos)
@@ -1737,11 +1782,18 @@ ftrace_pid_write(struct file *filp, const char __user *ubuf,
                clear_ftrace_pid_task(&ftrace_pid_trace);
 
        } else {
-               pid = find_get_pid(val);
+               /* swapper task is special */
+               if (!val) {
+                       pid = ftrace_swapper_pid;
+                       if (pid == ftrace_pid_trace)
+                               goto out;
+               } else {
+                       pid = find_get_pid(val);
 
-               if (pid == ftrace_pid_trace) {
-                       put_pid(pid);
-                       goto out;
+                       if (pid == ftrace_pid_trace) {
+                               put_pid(pid);
+                               goto out;
+                       }
                }
 
                if (ftrace_pid_trace)