tracing/ftrace: handle more than one stat file per tracer

Impact: new API for tracers

Make the stat tracing API reentrant. And also provide the new directory
/debugfs/tracing/trace_stat which will contain all the stat files for the
current active tracer.

Now a tracer will, if desired, want to provide a zero terminated array of
tracer_stat structures.
Each one contains the callbacks necessary for one stat file.
It have to provide at least a name for its stat file, an iterator with
stat_start/start_next callback and an output callback for one stat entry.

Also adapt the branch tracer to this new API.
We create two files "all" and "annotated" inside the /debugfs/tracing/trace_stat
directory, making the both stats simultaneously available instead of needing
to change an option to switch from one stat file to another.

The output of these stats haven't changed.

Changes in v2:

_ Apply the previous memory leak fix (rebase against tip/master)

Changes in v3:

_ Merge the patch that adapted the branch tracer to this Api in this patch to
  not break the kernel build.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 169 insertions, 61 deletions

diff --git a/kernel/trace/trace_stat.c b/kernel/trace/trace_stat.c
index f110ce9ce7fb..1515f9e7adfc 100644
--- a/kernel/trace/trace_stat.c
+++ b/kernel/trace/trace_stat.c
@@ -21,37 +21,87 @@ struct trace_stat_list {
         void *stat;
 };
 
-static LIST_HEAD(stat_list);
-
-/*
- * This is a copy of the current tracer to avoid racy
- * and dangerous output while the current tracer is
- * switched.
- */
-static struct tracer current_tracer;
+/* A stat session is the stats output in one file */
+struct tracer_stat_session {
+        struct tracer_stat *ts;
+        struct list_head stat_list;
+        struct mutex stat_mutex;
+};
 
-/*
- * Protect both the current tracer and the global
- * stat list.
- */
-static DEFINE_MUTEX(stat_list_mutex);
+/* All of the sessions currently in use. Each stat file embeed one session */
+static struct tracer_stat_session **all_stat_sessions;
+static int nb_sessions;
+static struct dentry *stat_dir, **stat_files;
 
 
-static void reset_stat_list(void)
+static void reset_stat_session(struct tracer_stat_session *session)
 {
         struct trace_stat_list *node, *next;
 
-        list_for_each_entry_safe(node, next, &stat_list, list)
+        list_for_each_entry_safe(node, next, &session->stat_list, list)
                 kfree(node);
 
-        INIT_LIST_HEAD(&stat_list);
+        INIT_LIST_HEAD(&session->stat_list);
 }
 
-void init_tracer_stat(struct tracer *trace)
+/* Called when a tracer is initialized */
+static int init_all_sessions(int nb, struct tracer_stat *ts)
 {
-        mutex_lock(&stat_list_mutex);
-        current_tracer = *trace;
-        mutex_unlock(&stat_list_mutex);
+        int i, j;
+        struct tracer_stat_session *session;
+
+        nb_sessions = 0;
+
+        if (all_stat_sessions) {
+                for (i = 0; i < nb_sessions; i++) {
+                        session = all_stat_sessions[i];
+                        reset_stat_session(session);
+                        mutex_destroy(&session->stat_mutex);
+                        kfree(session);
+                }
+        }
+        all_stat_sessions = kmalloc(sizeof(struct tracer_stat_session *) * nb,
+                                    GFP_KERNEL);
+        if (!all_stat_sessions)
+                return -ENOMEM;
+
+        for (i = 0; i < nb; i++) {
+                session = kmalloc(sizeof(struct tracer_stat_session) * nb,
+                                  GFP_KERNEL);
+                if (!session)
+                        goto free_sessions;
+
+                INIT_LIST_HEAD(&session->stat_list);
+                mutex_init(&session->stat_mutex);
+                session->ts = &ts[i];
+                all_stat_sessions[i] = session;
+        }
+        nb_sessions = nb;
+        return 0;
+
+free_sessions:
+
+        for (j = 0; j < i; j++)
+                kfree(all_stat_sessions[i]);
+
+        kfree(all_stat_sessions);
+        all_stat_sessions = NULL;
+
+        return -ENOMEM;
+}
+
+static int basic_tracer_stat_checks(struct tracer_stat *ts)
+{
+        int i;
+
+        if (!ts)
+                return 0;
+
+        for (i = 0; ts[i].name; i++) {
+                if (!ts[i].stat_start || !ts[i].stat_next || !ts[i].stat_show)
+                        return -EBUSY;
+        }
+        return i;
 }
 
 /*
@@ -69,22 +119,19 @@ static int dummy_cmp(void *p1, void *p2)
  * All of these copies and sorting are required on all opening
  * since the stats could have changed between two file sessions.
  */
-static int stat_seq_init(void)
+static int stat_seq_init(struct tracer_stat_session *session)
 {
         struct trace_stat_list *iter_entry, *new_entry;
+        struct tracer_stat *ts = session->ts;
         void *prev_stat;
         int ret = 0;
         int i;
 
-        mutex_lock(&stat_list_mutex);
-        reset_stat_list();
-
-        if (!current_tracer.stat_start || !current_tracer.stat_next ||
-                                        !current_tracer.stat_show)
-                goto exit;
+        mutex_lock(&session->stat_mutex);
+        reset_stat_session(session);
 
-        if (!current_tracer.stat_cmp)
-                current_tracer.stat_cmp = dummy_cmp;
+        if (!ts->stat_cmp)
+                ts->stat_cmp = dummy_cmp;
 
         /*
          * The first entry. Actually this is the second, but the first
@@ -97,9 +144,10 @@ static int stat_seq_init(void)
         }
 
         INIT_LIST_HEAD(&new_entry->list);
-        list_add(&new_entry->list, &stat_list);
-        new_entry->stat = current_tracer.stat_start();
 
+        list_add(&new_entry->list, &session->stat_list);
+
+        new_entry->stat = ts->stat_start();
         prev_stat = new_entry->stat;
 
         /*
@@ -114,15 +162,16 @@ static int stat_seq_init(void)
                 }
 
                 INIT_LIST_HEAD(&new_entry->list);
-                new_entry->stat = current_tracer.stat_next(prev_stat, i);
+                new_entry->stat = ts->stat_next(prev_stat, i);
 
                 /* End of insertion */
                 if (!new_entry->stat)
                         break;
 
-                list_for_each_entry(iter_entry, &stat_list, list) {
+                list_for_each_entry(iter_entry, &session->stat_list, list) {
+
                         /* Insertion with a descendent sorting */
-                        if (current_tracer.stat_cmp(new_entry->stat,
+                        if (ts->stat_cmp(new_entry->stat,
                                                 iter_entry->stat) > 0) {
 
                                 list_add_tail(&new_entry->list,
@@ -131,7 +180,7 @@ static int stat_seq_init(void)
 
                         /* The current smaller value */
                         } else if (list_is_last(&iter_entry->list,
-                                                &stat_list)) {
+                                                &session->stat_list)) {
                                 list_add(&new_entry->list, &iter_entry->list);
                                 break;
                         }
@@ -140,49 +189,49 @@ static int stat_seq_init(void)
                 prev_stat = new_entry->stat;
         }
 exit:
-        mutex_unlock(&stat_list_mutex);
+        mutex_unlock(&session->stat_mutex);
         return ret;
 
 exit_free_list:
-        reset_stat_list();
-        mutex_unlock(&stat_list_mutex);
+        reset_stat_session(session);
+        mutex_unlock(&session->stat_mutex);
         return ret;
 }
 
 
 static void *stat_seq_start(struct seq_file *s, loff_t *pos)
 {
-        struct list_head *l = (struct list_head *)s->private;
+        struct tracer_stat_session *session = s->private;
 
         /* Prevent from tracer switch or stat_list modification */
-        mutex_lock(&stat_list_mutex);
+        mutex_lock(&session->stat_mutex);
 
         /* If we are in the beginning of the file, print the headers */
-        if (!*pos && current_tracer.stat_headers)
-                current_tracer.stat_headers(s);
+        if (!*pos && session->ts->stat_headers)
+                session->ts->stat_headers(s);
 
-        return seq_list_start(l, *pos);
+        return seq_list_start(&session->stat_list, *pos);
 }
 
 static void *stat_seq_next(struct seq_file *s, void *p, loff_t *pos)
 {
-        struct list_head *l = (struct list_head *)s->private;
+        struct tracer_stat_session *session = s->private;
 
-        return seq_list_next(p, l, pos);
+        return seq_list_next(p, &session->stat_list, pos);
 }
 
-static void stat_seq_stop(struct seq_file *m, void *p)
+static void stat_seq_stop(struct seq_file *s, void *p)
 {
-        mutex_unlock(&stat_list_mutex);
+        struct tracer_stat_session *session = s->private;
+        mutex_unlock(&session->stat_mutex);
 }
 
 static int stat_seq_show(struct seq_file *s, void *v)
 {
-        struct trace_stat_list *entry;
-
-        entry = list_entry(v, struct trace_stat_list, list);
+        struct tracer_stat_session *session = s->private;
+        struct trace_stat_list *l = list_entry(v, struct trace_stat_list, list);
 
-        return current_tracer.stat_show(s, entry->stat);
+        return session->ts->stat_show(s, l->stat);
 }
 
 static const struct seq_operations trace_stat_seq_ops = {
@@ -192,15 +241,18 @@ static const struct seq_operations trace_stat_seq_ops = {
         .show = stat_seq_show
 };
 
+/* The session stat is refilled and resorted at each stat file opening */
 static int tracing_stat_open(struct inode *inode, struct file *file)
 {
         int ret;
 
+        struct tracer_stat_session *session = inode->i_private;
+
         ret = seq_open(file, &trace_stat_seq_ops);
         if (!ret) {
                 struct seq_file *m = file->private_data;
-                m->private = &stat_list;
-                ret = stat_seq_init();
+                m->private = session;
+                ret = stat_seq_init(session);
         }
 
         return ret;
@@ -212,9 +264,12 @@ static int tracing_stat_open(struct inode *inode, struct file *file)
  */
 static int tracing_stat_release(struct inode *i, struct file *f)
 {
-        mutex_lock(&stat_list_mutex);
-        reset_stat_list();
-        mutex_unlock(&stat_list_mutex);
+        struct tracer_stat_session *session = i->i_private;
+
+        mutex_lock(&session->stat_mutex);
+        reset_stat_session(session);
+        mutex_unlock(&session->stat_mutex);
+
         return 0;
 }
 
@@ -225,17 +280,70 @@ static const struct file_operations tracing_stat_fops = {
         .release        = tracing_stat_release
 };
 
+
+static void destroy_trace_stat_files(void)
+{
+        int i;
+
+        if (stat_files) {
+                for (i = 0; i < nb_sessions; i++)
+                        debugfs_remove(stat_files[i]);
+                kfree(stat_files);
+                stat_files = NULL;
+        }
+}
+
+static void init_trace_stat_files(void)
+{
+        int i;
+
+        if (!stat_dir || !nb_sessions)
+                return;
+
+        stat_files = kmalloc(sizeof(struct dentry *) * nb_sessions, GFP_KERNEL);
+
+        if (!stat_files) {
+                pr_warning("trace stat: not enough memory\n");
+                return;
+        }
+
+        for (i = 0; i < nb_sessions; i++) {
+                struct tracer_stat_session *session = all_stat_sessions[i];
+                stat_files[i] = debugfs_create_file(session->ts->name, 0644,
+                                                stat_dir,
+                                                session, &tracing_stat_fops);
+                if (!stat_files[i])
+                        pr_warning("cannot create %s entry\n",
+                                   session->ts->name);
+        }
+}
+
+void init_tracer_stat(struct tracer *trace)
+{
+        int nb = basic_tracer_stat_checks(trace->stats);
+
+        destroy_trace_stat_files();
+
+        if (nb < 0) {
+                pr_warning("stat tracing: missing stat callback on %s\n",
+                           trace->name);
+                return;
+        }
+        if (!nb)
+                return;
+
+        init_all_sessions(nb, trace->stats);
+        init_trace_stat_files();
+}
+
 static int __init tracing_stat_init(void)
 {
         struct dentry *d_tracing;
-        struct dentry *entry;
 
         d_tracing = tracing_init_dentry();
 
-        entry = debugfs_create_file("trace_stat", 0444, d_tracing,
-                                        NULL,
-                                    &tracing_stat_fops);
-        if (!entry)
+        stat_dir = debugfs_create_dir("trace_stat", d_tracing);
+        if (!stat_dir)
                 pr_warning("Could not create debugfs "
                            "'trace_stat' entry\n");
         return 0;