Skip to content

Commit

Permalink
ftrace: Create set_ftrace_notrace_pid to not trace tasks
Browse files Browse the repository at this point in the history 
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@goodmis.org>
  • Loading branch information
Steven Rostedt (VMware) committed Mar 27, 2020
1 parent 717e3f5 commit b3b1e6e
Show file tree
Hide file tree
Showing 4 changed files with 180 additions and 35 deletions.
181 changes: 158 additions & 23 deletions kernel/trace/ftrace.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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);
Expand Down Expand Up @@ -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
Expand All @@ -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
Expand All @@ -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)
Expand All @@ -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);
Expand Down Expand Up @@ -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;
Expand All @@ -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 {
Expand All @@ -7105,19 +7180,34 @@ 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
* event_mutex is held.
*/
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
Expand All @@ -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;

Expand All @@ -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);
}
Expand All @@ -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)
{
Expand All @@ -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,
Expand Down
20 changes: 14 additions & 6 deletions kernel/trace/trace.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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));
}

/**
Expand Down Expand Up @@ -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"
Expand Down
2 changes: 2 additions & 0 deletions kernel/trace/trace.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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,
Expand Down
Loading

0 comments on commit b3b1e6e

Please sign in to comment.