tracing: Add set_event_pid directory for future use

Create a tracing directory called set_event_pid, which currently has no
function, but will be used to filter all events for the tracing instance or
the pids that are added to the file.

The reason no functionality is added with this commit is that this commit
focuses on the creation and removal of the pids in a safe manner. And tests
can be made against this change to make sure things are correct before
hooking features to the list of pids.

Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.h

@@ -176,6 +176,12 @@ struct trace_options {
 	struct trace_option_dentry	*topts;
 };
 
+struct trace_pid_list {
+	unsigned int			nr_pids;
+	int				order;
+	pid_t				*pids;
+};
+
 /*
  * The trace array - an array of per-CPU trace arrays. This is the
  * highest level data structure that individual tracers deal with.
@@ -201,6 +207,7 @@ struct trace_array {
 	bool			allocated_snapshot;
 	unsigned long		max_latency;
 #endif
+	struct trace_pid_list	__rcu *filtered_pids;
 	/*
 	 * max_lock is used to protect the swapping of buffers
 	 * when taking a max snapshot. The buffers themselves are

kernel/trace/trace_events.c

@@ -15,8 +15,10 @@
 #include <linux/kthread.h>
 #include <linux/tracefs.h>
 #include <linux/uaccess.h>
+#include <linux/bsearch.h>
 #include <linux/module.h>
 #include <linux/ctype.h>
+#include <linux/sort.h>
 #include <linux/slab.h>
 #include <linux/delay.h>
 
@@ -445,6 +447,43 @@ static void ftrace_clear_events(struct trace_array *tr)
 	mutex_unlock(&event_mutex);
 }
 
+static int cmp_pid(const void *key, const void *elt)
+{
+	const pid_t *search_pid = key;
+	const pid_t *pid = elt;
+
+	if (*search_pid == *pid)
+		return 0;
+	if (*search_pid < *pid)
+		return -1;
+	return 1;
+}
+
+static void __ftrace_clear_event_pids(struct trace_array *tr)
+{
+	struct trace_pid_list *pid_list;
+
+	pid_list = rcu_dereference_protected(tr->filtered_pids,
+					     lockdep_is_held(&event_mutex));
+	if (!pid_list)
+		return;
+
+	rcu_assign_pointer(tr->filtered_pids, NULL);
+
+	/* Wait till all users are no longer using pid filtering */
+	synchronize_sched();
+
+	free_pages((unsigned long)pid_list->pids, pid_list->order);
+	kfree(pid_list);
+}
+
+static void ftrace_clear_event_pids(struct trace_array *tr)
+{
+	mutex_lock(&event_mutex);
+	__ftrace_clear_event_pids(tr);
+	mutex_unlock(&event_mutex);
+}
+
 static void __put_system(struct event_subsystem *system)
 {
 	struct event_filter *filter = system->filter;
@@ -777,6 +816,56 @@ static void t_stop(struct seq_file *m, void *p)
 	mutex_unlock(&event_mutex);
 }
 
+static void *p_start(struct seq_file *m, loff_t *pos)
+{
+	struct trace_pid_list *pid_list;
+	struct trace_array *tr = m->private;
+
+	/*
+	 * Grab the mutex, to keep calls to p_next() having the same
+	 * tr->filtered_pids as p_start() has.
+	 * If we just passed the tr->filtered_pids around, then RCU would
+	 * have been enough, but doing that makes things more complex.
+	 */
+	mutex_lock(&event_mutex);
+	rcu_read_lock_sched();
+
+	pid_list = rcu_dereference_sched(tr->filtered_pids);
+
+	if (!pid_list || *pos >= pid_list->nr_pids)
+		return NULL;
+
+	return (void *)&pid_list->pids[*pos];
+}
+
+static void p_stop(struct seq_file *m, void *p)
+{
+	rcu_read_unlock_sched();
+	mutex_unlock(&event_mutex);
+}
+
+static void *
+p_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->filtered_pids);
+
+	(*pos)++;
+
+	if (*pos >= pid_list->nr_pids)
+		return NULL;
+
+	return (void *)&pid_list->pids[*pos];
+}
+
+static int p_show(struct seq_file *m, void *v)
+{
+	pid_t *pid = v;
+
+	seq_printf(m, "%d\n", *pid);
+	return 0;
+}
+
 static ssize_t
 event_enable_read(struct file *filp, char __user *ubuf, size_t cnt,
 		  loff_t *ppos)
@@ -1334,8 +1423,165 @@ show_header(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
 	return r;
 }
 
+static int max_pids(struct trace_pid_list *pid_list)
+{
+	return (PAGE_SIZE << pid_list->order) / sizeof(pid_t);
+}
+
+static ssize_t
+ftrace_event_pid_write(struct file *file, const char __user *ubuf,
+		       size_t cnt, loff_t *ppos)
+{
+	struct seq_file *m = file->private_data;
+	struct trace_array *tr = m->private;
+	struct trace_pid_list *filtered_pids = NULL;
+	struct trace_pid_list *pid_list = NULL;
+	struct trace_parser parser;
+	unsigned long val;
+	loff_t this_pos;
+	ssize_t read = 0;
+	ssize_t ret = 0;
+	pid_t pid;
+	int i;
+
+	if (!cnt)
+		return 0;
+
+	ret = tracing_update_buffers();
+	if (ret < 0)
+		return ret;
+
+	if (trace_parser_get_init(&parser, EVENT_BUF_SIZE + 1))
+		return -ENOMEM;
+
+	mutex_lock(&event_mutex);
+	/*
+	 * Load as many pids into the array before doing a
+	 * swap from the tr->filtered_pids to the new list.
+	 */
+	while (cnt > 0) {
+
+		this_pos = 0;
+
+		ret = trace_get_user(&parser, ubuf, cnt, &this_pos);
+		if (ret < 0 || !trace_parser_loaded(&parser))
+			break;
+
+		read += ret;
+		ubuf += ret;
+		cnt -= ret;
+
+		parser.buffer[parser.idx] = 0;
+
+		ret = -EINVAL;
+		if (kstrtoul(parser.buffer, 0, &val))
+			break;
+		if (val > INT_MAX)
+			break;
+
+		pid = (pid_t)val;
+
+		ret = -ENOMEM;
+		if (!pid_list) {
+			pid_list = kmalloc(sizeof(*pid_list), GFP_KERNEL);
+			if (!pid_list)
+				break;
+
+			filtered_pids = rcu_dereference_protected(tr->filtered_pids,
+							lockdep_is_held(&event_mutex));
+			if (filtered_pids)
+				pid_list->order = filtered_pids->order;
+			else
+				pid_list->order = 0;
+
+			pid_list->pids = (void *)__get_free_pages(GFP_KERNEL,
+								  pid_list->order);
+			if (!pid_list->pids)
+				break;
+
+			if (filtered_pids) {
+				pid_list->nr_pids = filtered_pids->nr_pids;
+				memcpy(pid_list->pids, filtered_pids->pids,
+				       pid_list->nr_pids * sizeof(pid_t));
+			} else
+				pid_list->nr_pids = 0;
+		}
+
+		if (pid_list->nr_pids >= max_pids(pid_list)) {
+			pid_t *pid_page;
+
+			pid_page = (void *)__get_free_pages(GFP_KERNEL,
+							    pid_list->order + 1);
+			if (!pid_page)
+				break;
+			memcpy(pid_page, pid_list->pids,
+			       pid_list->nr_pids * sizeof(pid_t));
+			free_pages((unsigned long)pid_list->pids, pid_list->order);
+
+			pid_list->order++;
+			pid_list->pids = pid_page;
+		}
+
+		pid_list->pids[pid_list->nr_pids++] = pid;
+		trace_parser_clear(&parser);
+		ret = 0;
+	}
+	trace_parser_put(&parser);
+
+	if (ret < 0) {
+		if (pid_list)
+			free_pages((unsigned long)pid_list->pids, pid_list->order);
+		kfree(pid_list);
+		mutex_unlock(&event_mutex);
+		return ret;
+	}
+
+	if (!pid_list) {
+		mutex_unlock(&event_mutex);
+		return ret;
+	}
+
+	sort(pid_list->pids, pid_list->nr_pids, sizeof(pid_t), cmp_pid, NULL);
+
+	/* Remove duplicates */
+	for (i = 1; i < pid_list->nr_pids; i++) {
+		int start = i;
+
+		while (i < pid_list->nr_pids &&
+		       pid_list->pids[i - 1] == pid_list->pids[i])
+			i++;
+
+		if (start != i) {
+			if (i < pid_list->nr_pids) {
+				memmove(&pid_list->pids[start], &pid_list->pids[i],
+					(pid_list->nr_pids - i) * sizeof(pid_t));
+				pid_list->nr_pids -= i - start;
+				i = start;
+			} else
+				pid_list->nr_pids = start;
+		}
+	}
+
+	rcu_assign_pointer(tr->filtered_pids, pid_list);
+
+	mutex_unlock(&event_mutex);
+
+	if (filtered_pids) {
+		synchronize_sched();
+
+		free_pages((unsigned long)filtered_pids->pids, filtered_pids->order);
+		kfree(filtered_pids);
+	}
+
+	ret = read;
+	*ppos += read;
+
+	return ret;
+}
+
 static int ftrace_event_avail_open(struct inode *inode, struct file *file);
 static int ftrace_event_set_open(struct inode *inode, struct file *file);
+static int ftrace_event_set_pid_open(struct inode *inode, struct file *file);
 static int ftrace_event_release(struct inode *inode, struct file *file);
 
 static const struct seq_operations show_event_seq_ops = {
@@ -1352,6 +1598,13 @@ static const struct seq_operations show_set_event_seq_ops = {
 	.stop = t_stop,
 };
 
+static const struct seq_operations show_set_pid_seq_ops = {
+	.start = p_start,
+	.next = p_next,
+	.show = p_show,
+	.stop = p_stop,
+};
+
 static const struct file_operations ftrace_avail_fops = {
 	.open = ftrace_event_avail_open,
 	.read = seq_read,
@@ -1367,6 +1620,14 @@ static const struct file_operations ftrace_set_event_fops = {
 	.release = ftrace_event_release,
 };
 
+static const struct file_operations ftrace_set_event_pid_fops = {
+	.open = ftrace_event_set_pid_open,
+	.read = seq_read,
+	.write = ftrace_event_pid_write,
+	.llseek = seq_lseek,
+	.release = ftrace_event_release,
+};
+
 static const struct file_operations ftrace_enable_fops = {
 	.open = tracing_open_generic,
 	.read = event_enable_read,
@@ -1477,6 +1738,26 @@ ftrace_event_set_open(struct inode *inode, struct file *file)
 	return ret;
 }
 
+static int
+ftrace_event_set_pid_open(struct inode *inode, struct file *file)
+{
+	const struct seq_operations *seq_ops = &show_set_pid_seq_ops;
+	struct trace_array *tr = inode->i_private;
+	int ret;
+
+	if (trace_array_get(tr) < 0)
+		return -ENODEV;
+
+	if ((file->f_mode & FMODE_WRITE) &&
+	    (file->f_flags & O_TRUNC))
+		ftrace_clear_event_pids(tr);
+
+	ret = ftrace_event_open(inode, file, seq_ops);
+	if (ret < 0)
+		trace_array_put(tr);
+	return ret;
+}
+
 static struct event_subsystem *
 create_new_subsystem(const char *name)
 {
@@ -2471,6 +2752,9 @@ create_event_toplevel_files(struct dentry *parent, struct trace_array *tr)
 		return -ENOMEM;
 	}
 
+	entry = tracefs_create_file("set_event_pid", 0644, parent,
+				    tr, &ftrace_set_event_pid_fops);
+
 	/* ring buffer internal formats */
 	trace_create_file("header_page", 0444, d_events,
 			  ring_buffer_print_page_header,
@@ -2551,6 +2835,9 @@ int event_trace_del_tracer(struct trace_array *tr)
 	/* Disable any event triggers and associated soft-disabled events */
 	clear_event_triggers(tr);
 
+	/* Clear the pid list */
+	__ftrace_clear_event_pids(tr);
+
 	/* Disable any running events */
 	__ftrace_set_clr_event_nolock(tr, NULL, NULL, NULL, 0);