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Message-ID: <m1hc5vasye.fsf@frodo.ebiederm.org>
Date: Tue, 25 Nov 2008 22:42:49 -0800
From: ebiederm@...ssion.com (Eric W. Biederman)
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
Andrew Morton <akpm@...ux-foundation.org>,
Frederic Weisbecker <fweisbec@...il.com>,
containers@...ts.osdl.org,
Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
"Serge E. Hallyn" <serue@...ibm.com>,
Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 1/5] ftrace: add function tracing to single thread
Steven Rostedt <rostedt@...dmis.org> writes:
> From: Steven Rostedt <srostedt@...hat.com>
>
> Impact: feature to function trace a single thread
>
> This patch adds the ability to function trace a single thread.
> The file:
>
> /debugfs/tracing/set_ftrace_pid
>
> contains the pid to trace. Valid pids are any positive integer.
Please look below. Using find_get_pid causes this to use the
same logic as the rest of the kernel on what a valid pid is.
i.e. 0 is not a valid pid.
I believe I have sketched in what is needed to use the struct
pid api properly. Certainly enough for you to get the jist
of the idea.
> Writing any negative number to this file will disable the pid
> tracing and the function tracer will go back to tracing all of
> threads.
>
> This feature works with both static and dynamic function tracing.
>
> Signed-off-by: Steven Rostedt <srostedt@...hat.com>
> ---
> Documentation/ftrace.txt | 79 +++++++++++++++++
> kernel/trace/ftrace.c | 209 ++++++++++++++++++++++++++++++++++++++++------
> 2 files changed, 262 insertions(+), 26 deletions(-)
>
> diff --git a/Documentation/ftrace.txt b/Documentation/ftrace.txt
> index 35a78bc..de05042 100644
> --- a/Documentation/ftrace.txt
> +++ b/Documentation/ftrace.txt
> @@ -127,6 +127,8 @@ of ftrace. Here is a list of some of the key files:
> be traced. If a function exists in both set_ftrace_filter
> and set_ftrace_notrace, the function will _not_ be traced.
>
> + set_ftrace_pid: Have the function tracer only trace a single thread.
> +
> available_filter_functions: This lists the functions that ftrace
> has processed and can trace. These are the function
> names that you can pass to "set_ftrace_filter" or
> @@ -1073,6 +1075,83 @@ For simple one time traces, the above is sufficent. For
> anything else,
> a search through /proc/mounts may be needed to find where the debugfs
> file-system is mounted.
>
> +
> +Single thread tracing
> +---------------------
> +
> +By writing into /debug/tracing/set_ftrace_pid you can trace a
> +single thread. For example:
> +
> +# cat /debug/tracing/set_ftrace_pid
> +no pid
> +# echo 3111 > /debug/tracing/set_ftrace_pid
> +# cat /debug/tracing/set_ftrace_pid
> +3111
> +# echo function > /debug/tracing/current_tracer
> +# cat /debug/tracing/trace | head
> + # tracer: function
> + #
> + # TASK-PID CPU# TIMESTAMP FUNCTION
> + # | | | | |
> + yum-updatesd-3111 [003] 1637.254676: finish_task_switch <-thread_return
> + yum-updatesd-3111 [003] 1637.254681: hrtimer_cancel <-schedule_hrtimeout_range
> + yum-updatesd-3111 [003] 1637.254682: hrtimer_try_to_cancel <-hrtimer_cancel
> + yum-updatesd-3111 [003] 1637.254683: lock_hrtimer_base <-hrtimer_try_to_cancel
> + yum-updatesd-3111 [003] 1637.254685: fget_light <-do_sys_poll
> + yum-updatesd-3111 [003] 1637.254686: pipe_poll <-do_sys_poll
> +# echo -1 > /debug/tracing/set_ftrace_pid
> +# cat /debug/tracing/trace |head
> + # tracer: function
> + #
> + # TASK-PID CPU# TIMESTAMP FUNCTION
> + # | | | | |
> + ##### CPU 3 buffer started ####
> + yum-updatesd-3111 [003] 1701.957688: free_poll_entry <-poll_freewait
> + yum-updatesd-3111 [003] 1701.957689: remove_wait_queue <-free_poll_entry
> + yum-updatesd-3111 [003] 1701.957691: fput <-free_poll_entry
> + yum-updatesd-3111 [003] 1701.957692: audit_syscall_exit <-sysret_audit
> + yum-updatesd-3111 [003] 1701.957693: path_put <-audit_syscall_exit
> +
> +If you want to trace a function when executing, you could use
> +something like this simple program:
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <fcntl.h>
> +#include <unistd.h>
> +
> +int main (int argc, char **argv)
> +{
> + if (argc < 1)
> + exit(-1);
> +
> + if (fork() > 0) {
> + int fd, ffd;
> + char line[64];
> + int s;
> +
> + ffd = open("/debug/tracing/current_tracer", O_WRONLY);
> + if (ffd < 0)
> + exit(-1);
> + write(ffd, "nop", 3);
> +
> + fd = open("/debug/tracing/set_ftrace_pid", O_WRONLY);
> + s = sprintf(line, "%d\n", getpid());
> + write(fd, line, s);
> +
> + write(ffd, "function", 8);
> +
> + close(fd);
> + close(ffd);
> +
> + execvp(argv[1], argv+1);
> + }
> +
> + return 0;
> +}
> +
> dynamic ftrace
> --------------
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 7e2d3b9..00d98c6 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;
>
> +/* ftrace_pid_trace >= 0 will only trace threads with this pid */
> +static int ftrace_pid_trace = -1;
Why not?
static struct pid *ftrace_pid_trace = NULL;
> +
> /* Quick disabling of function tracer. */
> int function_trace_stop;
>
> @@ -61,6 +64,7 @@ static int ftrace_disabled __read_mostly;
>
> static DEFINE_SPINLOCK(ftrace_lock);
> static DEFINE_MUTEX(ftrace_sysctl_lock);
> +static DEFINE_MUTEX(ftrace_start_lock);
>
> static struct ftrace_ops ftrace_list_end __read_mostly =
> {
> @@ -70,6 +74,7 @@ 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;
> +ftrace_func_t ftrace_pid_function __read_mostly = ftrace_stub;
>
> static void ftrace_list_func(unsigned long ip, unsigned long parent_ip)
> {
> @@ -86,6 +91,21 @@ static void ftrace_list_func(unsigned long ip, unsigned long
> parent_ip)
> };
> }
>
> +static void ftrace_pid_func(unsigned long ip, unsigned long parent_ip)
> +{
> + if (current->pid != ftrace_pid_trace)
> + return;
And why not?
if (task_pid(current) != ftrace_pid_trace)
return;
Racy or not. This is only comparing a different field in struct task_struct.
So there should be not real difference.
> +
> + ftrace_pid_function(ip, parent_ip);
> +}
> +
> +static void set_ftrace_pid_function(ftrace_func_t func)
> +{
> + /* do not set ftrace_pid_function to itself! */
> + if (func != ftrace_pid_func)
> + ftrace_pid_function = func;
> +}
> +
> /**
> * clear_ftrace_function - reset the ftrace function
> *
> @@ -96,6 +116,7 @@ void clear_ftrace_function(void)
> {
> ftrace_trace_function = ftrace_stub;
> __ftrace_trace_function = ftrace_stub;
> + ftrace_pid_function = ftrace_stub;
> }
>
> #ifndef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST
> @@ -128,20 +149,26 @@ static int __register_ftrace_function(struct ftrace_ops
> *ops)
> ftrace_list = ops;
>
> if (ftrace_enabled) {
> + ftrace_func_t func;
> +
> + if (ops->next == &ftrace_list_end)
> + func = ops->func;
> + else
> + func = ftrace_list_func;
> +
> + if (ftrace_pid_trace >= 0) {
And why not:
if (ftrace_pid_trace) {
> + set_ftrace_pid_function(func);
> + func = ftrace_pid_func;
> + }
> +
> /*
> * 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;
> + ftrace_trace_function = func;
> #else
> - if (ops->next == &ftrace_list_end)
> - __ftrace_trace_function = ops->func;
> - else
> - __ftrace_trace_function = ftrace_list_func;
> + __ftrace_trace_function = func;
> ftrace_trace_function = ftrace_test_stop_func;
> #endif
> }
> @@ -182,8 +209,19 @@ static int __unregister_ftrace_function(struct ftrace_ops
> *ops)
>
> if (ftrace_enabled) {
> /* If we only have one func left, then call that directly */
> - if (ftrace_list->next == &ftrace_list_end)
> - ftrace_trace_function = ftrace_list->func;
> + if (ftrace_list->next == &ftrace_list_end) {
> + ftrace_func_t func = ftrace_list->func;
> +
> + if (ftrace_pid_trace >= 0) {
And why not:
if (ftrace_pid_trace) {
> + set_ftrace_pid_function(func);
> + func = ftrace_pid_func;
> + }
> +#ifdef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST
> + ftrace_trace_function = func;
> +#else
> + __ftrace_trace_function = func;
> +#endif
> + }
> }
>
> out:
> @@ -192,6 +230,38 @@ static int __unregister_ftrace_function(struct ftrace_ops
> *ops)
> return ret;
> }
>
> +static void ftrace_update_pid_func(void)
> +{
> + ftrace_func_t func;
> +
> + /* should not be called from interrupt context */
> + spin_lock(&ftrace_lock);
> +
> + if (ftrace_trace_function == ftrace_stub)
> + goto out;
> +
> + func = ftrace_trace_function;
> +
> + if (ftrace_pid_trace >= 0) {
And why not:
if (ftrace_pid_trace) {
> + set_ftrace_pid_function(func);
> + func = ftrace_pid_func;
> + } else {
> + if (func != ftrace_pid_func)
> + goto out;
> +
> + set_ftrace_pid_function(func);
> + }
> +
> +#ifdef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST
> + ftrace_trace_function = func;
> +#else
> + __ftrace_trace_function = func;
> +#endif
> +
> + out:
> + spin_unlock(&ftrace_lock);
> +}
> +
> #ifdef CONFIG_DYNAMIC_FTRACE
> #ifndef CONFIG_FTRACE_MCOUNT_RECORD
> # error Dynamic ftrace depends on MCOUNT_RECORD
> @@ -545,7 +615,19 @@ static void ftrace_run_update_code(int command)
>
> static ftrace_func_t saved_ftrace_func;
> static int ftrace_start_up;
> -static DEFINE_MUTEX(ftrace_start_lock);
> +
> +static void ftrace_startup_enable(int command)
> +{
> + if (saved_ftrace_func != ftrace_trace_function) {
> + saved_ftrace_func = ftrace_trace_function;
> + command |= FTRACE_UPDATE_TRACE_FUNC;
> + }
> +
> + if (!command || !ftrace_enabled)
> + return;
> +
> + ftrace_run_update_code(command);
> +}
>
> static void ftrace_startup(void)
> {
> @@ -558,16 +640,8 @@ static void ftrace_startup(void)
> ftrace_start_up++;
> command |= FTRACE_ENABLE_CALLS;
>
> - if (saved_ftrace_func != ftrace_trace_function) {
> - saved_ftrace_func = ftrace_trace_function;
> - command |= FTRACE_UPDATE_TRACE_FUNC;
> - }
> -
> - if (!command || !ftrace_enabled)
> - goto out;
> + ftrace_startup_enable(command);
>
> - ftrace_run_update_code(command);
> - out:
> mutex_unlock(&ftrace_start_lock);
> }
>
> @@ -1262,13 +1336,10 @@ static struct file_operations ftrace_notrace_fops = {
> .release = ftrace_notrace_release,
> };
>
> -static __init int ftrace_init_debugfs(void)
> +static __init int ftrace_init_dyn_debugfs(struct dentry *d_tracer)
> {
> - struct dentry *d_tracer;
> struct dentry *entry;
>
> - d_tracer = tracing_init_dentry();
> -
> entry = debugfs_create_file("available_filter_functions", 0444,
> d_tracer, NULL, &ftrace_avail_fops);
> if (!entry)
> @@ -1295,8 +1366,6 @@ static __init int ftrace_init_debugfs(void)
> return 0;
> }
>
> -fs_initcall(ftrace_init_debugfs);
> -
> static int ftrace_convert_nops(struct module *mod,
> unsigned long *start,
> unsigned long *end)
> @@ -1382,12 +1451,100 @@ static int __init ftrace_nodyn_init(void)
> }
> device_initcall(ftrace_nodyn_init);
>
> +static inline int ftrace_init_dyn_debugfs(struct dentry *d_tracer) { return 0;
> }
> +static inline void ftrace_startup_enable(int command) { }
> # define ftrace_startup() do { } while (0)
> # define ftrace_shutdown() do { } while (0)
> # define ftrace_startup_sysctl() do { } while (0)
> # define ftrace_shutdown_sysctl() do { } while (0)
> #endif /* CONFIG_DYNAMIC_FTRACE */
>
> +static ssize_t
> +ftrace_pid_read(struct file *file, char __user *ubuf,
> + size_t cnt, loff_t *ppos)
> +{
> + char buf[64];
> + int r;
> +
> + if (ftrace_pid_trace >= 0)
> + r = sprintf(buf, "%u\n", ftrace_pid_trace);
And why not:
if (ftrace_pid_trace)
r = sprintf(buf, "%u\n", pid_vmr(ftrace_pid_trace))
> + else
> + r = sprintf(buf, "no pid\n");
> +
> + return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
> +}
> +
> +static ssize_t
> +ftrace_pid_write(struct file *filp, const char __user *ubuf,
> + size_t cnt, loff_t *ppos)
> +{
> + char buf[64];
> + long val;
> + int ret;
> +
> + if (cnt >= sizeof(buf))
> + return -EINVAL;
> +
> + if (copy_from_user(&buf, ubuf, cnt))
> + return -EFAULT;
> +
> + buf[cnt] = 0;
> +
> + ret = strict_strtol(buf, 10, &val);
> + if (ret < 0)
> + return ret;
Why not?
pid = find_get_pid(ret);
mutex_lock(&ftrace_start_lock);
if (pid == ftrace_pid_trace)
goto out;
struct pid *tmp;
tmp = ftrace_pid_trace;
ftrace_pid_trace = pid;
pid = tmp;
/* update the function call */
ftrace_update_pid_func();
ftrace_startup_enable(0);
out:
mutex_unlock(&ftrace_start_lock);
put_pid(pid);
> +
> + mutex_lock(&ftrace_start_lock);
> + if (ret < 0) {
> + /* disable pid tracing */
> + if (ftrace_pid_trace < 0)
> + goto out;
> + ftrace_pid_trace = -1;
> +
> + } else {
> +
> + if (ftrace_pid_trace == val)
> + goto out;
> +
> + ftrace_pid_trace = val;
> + }
> +
> + /* update the function call */
> + ftrace_update_pid_func();
> + ftrace_startup_enable(0);
> +
> + out:
> + mutex_unlock(&ftrace_start_lock);
> +
> + return cnt;
> +}
> +
> +static struct file_operations ftrace_pid_fops = {
> + .read = ftrace_pid_read,
> + .write = ftrace_pid_write,
> +};
> +
> +static __init int ftrace_init_debugfs(void)
> +{
> + struct dentry *d_tracer;
> + struct dentry *entry;
> +
> + d_tracer = tracing_init_dentry();
> + if (!d_tracer)
> + return 0;
> +
> + ftrace_init_dyn_debugfs(d_tracer);
> +
> + entry = debugfs_create_file("set_ftrace_pid", 0644, d_tracer,
> + NULL, &ftrace_pid_fops);
> + if (!entry)
> + pr_warning("Could not create debugfs "
> + "'set_ftrace_pid' entry\n");
> + return 0;
> +}
> +
> +fs_initcall(ftrace_init_debugfs);
> +
> /**
> * ftrace_kill - kill ftrace
> *
> --
> 1.5.6.5
>
> --
--
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