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>

1 files changed, 63 insertions, 11 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 10b1d7c1b1dd..eb57dc1ea097 100644
--- 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)