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SubjectRe: [PATCH 3/3] ftrace: add ability to only trace swapper tasks
Date
Steven Rostedt <rostedt@goodmis.org> writes:

> From: Steven Rostedt <srostedt@redhat.com>
>
> 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.

Ok. Nits below.

> Signed-off-by: Steven Rostedt <srostedt@redhat.com>
> ---
> kernel/trace/ftrace.c | 74 +++++++++++++++++++++++++++++++++++++++++-------
> 1 files changed, 63 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 10b1d7c..eb57dc1 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;

The initializer should be spelled &init_struct_pid instead of (struct pid *)1;

Except for the special case of finding this unhashed pid, by making the
attach_pid(p, PIDTYPE_PID, pid) unconditional in copy_process, you can
make the rest of the special cases go away.

Eric

>
> /* 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)
> --
> 1.5.6.5
>
> --


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