[for-next][PATCH 17/21] ftrace: Create set_ftrace_notrace_pid to not trace tasks

From: Steven Rostedt
Date: Sun Mar 29 2020 - 14:44:00 EST

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From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>

There's currently a way to select a task that should only be traced by
functions, but there's no way to select a task not to be traced by the
function tracer. Add a set_ftrace_notrace_pid file that acts the same as
set_ftrace_pid (and is also affected by function-fork), but the task pids in
this file will not be traced even if they are listed in the set_ftrace_pid
file. This makes it easy for tools like trace-cmd to "hide" itself from the
function tracer when it is recording other tasks.

Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
kernel/trace/ftrace.c | 181 +++++++++++++++++++++++++++++++-----
kernel/trace/trace.c | 20 ++--
kernel/trace/trace.h | 2 +
kernel/trace/trace_events.c | 12 +--
4 files changed, 180 insertions(+), 35 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 34ae736cb1f8..7239d9acd09f 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -102,7 +102,7 @@ static bool ftrace_pids_enabled(struct ftrace_ops *ops)

tr = ops->private;

- return tr->function_pids != NULL;
+ return tr->function_pids != NULL || tr->function_no_pids != NULL;
}

static void ftrace_update_trampoline(struct ftrace_ops *ops);
@@ -6931,10 +6931,12 @@ ftrace_filter_pid_sched_switch_probe(void *data, bool preempt,
{
struct trace_array *tr = data;
struct trace_pid_list *pid_list;
+ struct trace_pid_list *no_pid_list;

pid_list = rcu_dereference_sched(tr->function_pids);
+ no_pid_list = rcu_dereference_sched(tr->function_no_pids);

- if (trace_ignore_this_task(pid_list, next))
+ if (trace_ignore_this_task(pid_list, no_pid_list, next))
this_cpu_write(tr->array_buffer.data->ftrace_ignore_pid,
FTRACE_PID_IGNORE);
else
@@ -6952,6 +6954,9 @@ ftrace_pid_follow_sched_process_fork(void *data,

pid_list = rcu_dereference_sched(tr->function_pids);
trace_filter_add_remove_task(pid_list, self, task);
+
+ pid_list = rcu_dereference_sched(tr->function_no_pids);
+ trace_filter_add_remove_task(pid_list, self, task);
}

static void
@@ -6962,6 +6967,9 @@ ftrace_pid_follow_sched_process_exit(void *data, struct task_struct *task)

pid_list = rcu_dereference_sched(tr->function_pids);
trace_filter_add_remove_task(pid_list, NULL, task);
+
+ pid_list = rcu_dereference_sched(tr->function_no_pids);
+ trace_filter_add_remove_task(pid_list, NULL, task);
}

void ftrace_pid_follow_fork(struct trace_array *tr, bool enable)
@@ -6979,42 +6987,64 @@ void ftrace_pid_follow_fork(struct trace_array *tr, bool enable)
}
}

-static void clear_ftrace_pids(struct trace_array *tr)
+enum {
+ TRACE_PIDS = BIT(0),
+ TRACE_NO_PIDS = BIT(1),
+};
+
+static void clear_ftrace_pids(struct trace_array *tr, int type)
{
struct trace_pid_list *pid_list;
+ struct trace_pid_list *no_pid_list;
int cpu;

pid_list = rcu_dereference_protected(tr->function_pids,
lockdep_is_held(&ftrace_lock));
- if (!pid_list)
+ no_pid_list = rcu_dereference_protected(tr->function_no_pids,
+ lockdep_is_held(&ftrace_lock));
+
+ /* Make sure there's something to do */
+ if (!(((type & TRACE_PIDS) && pid_list) ||
+ ((type & TRACE_NO_PIDS) && no_pid_list)))
return;

- unregister_trace_sched_switch(ftrace_filter_pid_sched_switch_probe, tr);
+ /* See if the pids still need to be checked after this */
+ if (!((!(type & TRACE_PIDS) && pid_list) ||
+ (!(type & TRACE_NO_PIDS) && no_pid_list))) {
+ unregister_trace_sched_switch(ftrace_filter_pid_sched_switch_probe, tr);
+ for_each_possible_cpu(cpu)
+ per_cpu_ptr(tr->array_buffer.data, cpu)->ftrace_ignore_pid = FTRACE_PID_TRACE;
+ }

- for_each_possible_cpu(cpu)
- per_cpu_ptr(tr->array_buffer.data, cpu)->ftrace_ignore_pid = FTRACE_PID_TRACE;
+ if (type & TRACE_PIDS)
+ rcu_assign_pointer(tr->function_pids, NULL);

- rcu_assign_pointer(tr->function_pids, NULL);
+ if (type & TRACE_NO_PIDS)
+ rcu_assign_pointer(tr->function_no_pids, NULL);

/* Wait till all users are no longer using pid filtering */
synchronize_rcu();

- trace_free_pid_list(pid_list);
+ if ((type & TRACE_PIDS) && pid_list)
+ trace_free_pid_list(pid_list);
+
+ if ((type & TRACE_NO_PIDS) && no_pid_list)
+ trace_free_pid_list(no_pid_list);
}

void ftrace_clear_pids(struct trace_array *tr)
{
mutex_lock(&ftrace_lock);

- clear_ftrace_pids(tr);
+ clear_ftrace_pids(tr, TRACE_PIDS | TRACE_NO_PIDS);

mutex_unlock(&ftrace_lock);
}

-static void ftrace_pid_reset(struct trace_array *tr)
+static void ftrace_pid_reset(struct trace_array *tr, int type)
{
mutex_lock(&ftrace_lock);
- clear_ftrace_pids(tr);
+ clear_ftrace_pids(tr, type);

ftrace_update_pid_func();
ftrace_startup_all(0);
@@ -7078,9 +7108,45 @@ static const struct seq_operations ftrace_pid_sops = {
.show = fpid_show,
};

-static int
-ftrace_pid_open(struct inode *inode, struct file *file)
+static void *fnpid_start(struct seq_file *m, loff_t *pos)
+ __acquires(RCU)
+{
+ struct trace_pid_list *pid_list;
+ struct trace_array *tr = m->private;
+
+ mutex_lock(&ftrace_lock);
+ rcu_read_lock_sched();
+
+ pid_list = rcu_dereference_sched(tr->function_no_pids);
+
+ if (!pid_list)
+ return !(*pos) ? FTRACE_NO_PIDS : NULL;
+
+ return trace_pid_start(pid_list, pos);
+}
+
+static void *fnpid_next(struct seq_file *m, void *v, loff_t *pos)
{
+ struct trace_array *tr = m->private;
+ struct trace_pid_list *pid_list = rcu_dereference_sched(tr->function_no_pids);
+
+ if (v == FTRACE_NO_PIDS) {
+ (*pos)++;
+ return NULL;
+ }
+ return trace_pid_next(pid_list, v, pos);
+}
+
+static const struct seq_operations ftrace_no_pid_sops = {
+ .start = fnpid_start,
+ .next = fnpid_next,
+ .stop = fpid_stop,
+ .show = fpid_show,
+};
+
+static int pid_open(struct inode *inode, struct file *file, int type)
+{
+ const struct seq_operations *seq_ops;
struct trace_array *tr = inode->i_private;
struct seq_file *m;
int ret = 0;
@@ -7091,9 +7157,18 @@ ftrace_pid_open(struct inode *inode, struct file *file)

if ((file->f_mode & FMODE_WRITE) &&
(file->f_flags & O_TRUNC))
- ftrace_pid_reset(tr);
+ ftrace_pid_reset(tr, type);
+
+ switch (type) {
+ case TRACE_PIDS:
+ seq_ops = &ftrace_pid_sops;
+ break;
+ case TRACE_NO_PIDS:
+ seq_ops = &ftrace_no_pid_sops;
+ break;
+ }

- ret = seq_open(file, &ftrace_pid_sops);
+ ret = seq_open(file, seq_ops);
if (ret < 0) {
trace_array_put(tr);
} else {
@@ -7105,10 +7180,23 @@ ftrace_pid_open(struct inode *inode, struct file *file)
return ret;
}

+static int
+ftrace_pid_open(struct inode *inode, struct file *file)
+{
+ return pid_open(inode, file, TRACE_PIDS);
+}
+
+static int
+ftrace_no_pid_open(struct inode *inode, struct file *file)
+{
+ return pid_open(inode, file, TRACE_NO_PIDS);
+}
+
static void ignore_task_cpu(void *data)
{
struct trace_array *tr = data;
struct trace_pid_list *pid_list;
+ struct trace_pid_list *no_pid_list;

/*
* This function is called by on_each_cpu() while the
@@ -7116,8 +7204,10 @@ static void ignore_task_cpu(void *data)
*/
pid_list = rcu_dereference_protected(tr->function_pids,
mutex_is_locked(&ftrace_lock));
+ no_pid_list = rcu_dereference_protected(tr->function_no_pids,
+ mutex_is_locked(&ftrace_lock));

- if (trace_ignore_this_task(pid_list, current))
+ if (trace_ignore_this_task(pid_list, no_pid_list, current))
this_cpu_write(tr->array_buffer.data->ftrace_ignore_pid,
FTRACE_PID_IGNORE);
else
@@ -7126,12 +7216,13 @@ static void ignore_task_cpu(void *data)
}

static ssize_t
-ftrace_pid_write(struct file *filp, const char __user *ubuf,
- size_t cnt, loff_t *ppos)
+pid_write(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos, int type)
{
struct seq_file *m = filp->private_data;
struct trace_array *tr = m->private;
- struct trace_pid_list *filtered_pids = NULL;
+ struct trace_pid_list *filtered_pids;
+ struct trace_pid_list *other_pids;
struct trace_pid_list *pid_list;
ssize_t ret;

@@ -7140,19 +7231,39 @@ ftrace_pid_write(struct file *filp, const char __user *ubuf,

mutex_lock(&ftrace_lock);

- filtered_pids = rcu_dereference_protected(tr->function_pids,
+ switch (type) {
+ case TRACE_PIDS:
+ filtered_pids = rcu_dereference_protected(tr->function_pids,
lockdep_is_held(&ftrace_lock));
+ other_pids = rcu_dereference_protected(tr->function_no_pids,
+ lockdep_is_held(&ftrace_lock));
+ break;
+ case TRACE_NO_PIDS:
+ filtered_pids = rcu_dereference_protected(tr->function_no_pids,
+ lockdep_is_held(&ftrace_lock));
+ other_pids = rcu_dereference_protected(tr->function_pids,
+ lockdep_is_held(&ftrace_lock));
+ break;
+ }

ret = trace_pid_write(filtered_pids, &pid_list, ubuf, cnt);
if (ret < 0)
goto out;

- rcu_assign_pointer(tr->function_pids, pid_list);
+ switch (type) {
+ case TRACE_PIDS:
+ rcu_assign_pointer(tr->function_pids, pid_list);
+ break;
+ case TRACE_NO_PIDS:
+ rcu_assign_pointer(tr->function_no_pids, pid_list);
+ break;
+ }
+

if (filtered_pids) {
synchronize_rcu();
trace_free_pid_list(filtered_pids);
- } else if (pid_list) {
+ } else if (pid_list && !other_pids) {
/* Register a probe to set whether to ignore the tracing of a task */
register_trace_sched_switch(ftrace_filter_pid_sched_switch_probe, tr);
}
@@ -7175,6 +7286,20 @@ ftrace_pid_write(struct file *filp, const char __user *ubuf,
return ret;
}

+static ssize_t
+ftrace_pid_write(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ return pid_write(filp, ubuf, cnt, ppos, TRACE_PIDS);
+}
+
+static ssize_t
+ftrace_no_pid_write(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ return pid_write(filp, ubuf, cnt, ppos, TRACE_NO_PIDS);
+}
+
static int
ftrace_pid_release(struct inode *inode, struct file *file)
{
@@ -7193,10 +7318,20 @@ static const struct file_operations ftrace_pid_fops = {
.release = ftrace_pid_release,
};

+static const struct file_operations ftrace_no_pid_fops = {
+ .open = ftrace_no_pid_open,
+ .write = ftrace_no_pid_write,
+ .read = seq_read,
+ .llseek = tracing_lseek,
+ .release = ftrace_pid_release,
+};
+
void ftrace_init_tracefs(struct trace_array *tr, struct dentry *d_tracer)
{
trace_create_file("set_ftrace_pid", 0644, d_tracer,
tr, &ftrace_pid_fops);
+ trace_create_file("set_ftrace_notrace_pid", 0644, d_tracer,
+ tr, &ftrace_no_pid_fops);
}

void __init ftrace_init_tracefs_toplevel(struct trace_array *tr,
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5e634b9c1e0a..6519b7afc499 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -386,16 +386,22 @@ trace_find_filtered_pid(struct trace_pid_list *filtered_pids, pid_t search_pid)
* Returns false if @task should be traced.
*/
bool
-trace_ignore_this_task(struct trace_pid_list *filtered_pids, struct task_struct *task)
+trace_ignore_this_task(struct trace_pid_list *filtered_pids,
+ struct trace_pid_list *filtered_no_pids,
+ struct task_struct *task)
{
/*
- * Return false, because if filtered_pids does not exist,
- * all pids are good to trace.
+ * If filterd_no_pids is not empty, and the task's pid is listed
+ * in filtered_no_pids, then return true.
+ * Otherwise, if filtered_pids is empty, that means we can
+ * trace all tasks. If it has content, then only trace pids
+ * within filtered_pids.
*/
- if (!filtered_pids)
- return false;

- return !trace_find_filtered_pid(filtered_pids, task->pid);
+ return (filtered_pids &&
+ !trace_find_filtered_pid(filtered_pids, task->pid)) ||
+ (filtered_no_pids &&
+ trace_find_filtered_pid(filtered_no_pids, task->pid));
}

/**
@@ -5013,6 +5019,8 @@ static const char readme_msg[] =
#ifdef CONFIG_FUNCTION_TRACER
" set_ftrace_pid\t- Write pid(s) to only function trace those pids\n"
"\t\t (function)\n"
+ " set_ftrace_notrace_pid\t- Write pid(s) to not function trace those pids\n"
+ "\t\t (function)\n"
#endif
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
" set_graph_function\t- Trace the nested calls of a function (function_graph)\n"
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index fdc72f5f0bb0..6b5ff5adb4ad 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -331,6 +331,7 @@ struct trace_array {
#ifdef CONFIG_FUNCTION_TRACER
struct ftrace_ops *ops;
struct trace_pid_list __rcu *function_pids;
+ struct trace_pid_list __rcu *function_no_pids;
#ifdef CONFIG_DYNAMIC_FTRACE
/* All of these are protected by the ftrace_lock */
struct list_head func_probes;
@@ -782,6 +783,7 @@ extern int pid_max;
bool trace_find_filtered_pid(struct trace_pid_list *filtered_pids,
pid_t search_pid);
bool trace_ignore_this_task(struct trace_pid_list *filtered_pids,
+ struct trace_pid_list *filtered_no_pids,
struct task_struct *task);
void trace_filter_add_remove_task(struct trace_pid_list *pid_list,
struct task_struct *self,
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index f38234ecea18..c196d0dc5871 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -549,8 +549,8 @@ event_filter_pid_sched_switch_probe_pre(void *data, bool preempt,
pid_list = rcu_dereference_sched(tr->filtered_pids);

this_cpu_write(tr->array_buffer.data->ignore_pid,
- trace_ignore_this_task(pid_list, prev) &&
- trace_ignore_this_task(pid_list, next));
+ trace_ignore_this_task(pid_list, NULL, prev) &&
+ trace_ignore_this_task(pid_list, NULL, next));
}

static void
@@ -563,7 +563,7 @@ event_filter_pid_sched_switch_probe_post(void *data, bool preempt,
pid_list = rcu_dereference_sched(tr->filtered_pids);

this_cpu_write(tr->array_buffer.data->ignore_pid,
- trace_ignore_this_task(pid_list, next));
+ trace_ignore_this_task(pid_list, NULL, next));
}

static void
@@ -579,7 +579,7 @@ event_filter_pid_sched_wakeup_probe_pre(void *data, struct task_struct *task)
pid_list = rcu_dereference_sched(tr->filtered_pids);

this_cpu_write(tr->array_buffer.data->ignore_pid,
- trace_ignore_this_task(pid_list, task));
+ trace_ignore_this_task(pid_list, NULL, task));
}

static void
@@ -596,7 +596,7 @@ event_filter_pid_sched_wakeup_probe_post(void *data, struct task_struct *task)

/* Set tracing if current is enabled */
this_cpu_write(tr->array_buffer.data->ignore_pid,
- trace_ignore_this_task(pid_list, current));
+ trace_ignore_this_task(pid_list, NULL, current));
}

static void __ftrace_clear_event_pids(struct trace_array *tr)
@@ -1597,7 +1597,7 @@ static void ignore_task_cpu(void *data)
mutex_is_locked(&event_mutex));

this_cpu_write(tr->array_buffer.data->ignore_pid,
- trace_ignore_this_task(pid_list, current));
+ trace_ignore_this_task(pid_list, NULL, current));
}

static ssize_t
--
2.25.1

Next message: Steven Rostedt: "[for-next][PATCH 21/21] tracing: Add documentation on set_ftrace_notrace_pid and set_event_notrace_pid"
Previous message: Steven Rostedt: "[for-next][PATCH 02/21] selftest/ftrace: Fix function trigger test to handle trace not disabling the tracer"
In reply to: Steven Rostedt: "[for-next][PATCH 02/21] selftest/ftrace: Fix function trigger test to handle trace not disabling the tracer"
Next in thread: Steven Rostedt: "[for-next][PATCH 21/21] tracing: Add documentation on set_ftrace_notrace_pid and set_event_notrace_pid"
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