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Date: Mon, 5 Jan 2009 15:53:38 -0500 (EST)
From: Steven Rostedt <rostedt@...dmis.org>
To: Frederic Weisbecker <fweisbec@...il.com>
cc: Ingo Molnar <mingo@...e.hu>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Pekka Enberg <penberg@...helsinki.fi>,
Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
Subject: Re: [PATCH 1/2] tracing/ftrace: handle more than one stat file per
tracer
On Wed, 31 Dec 2008, Frederic Weisbecker wrote:
> 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.
>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> ---
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 46677ea..b093f36 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -335,6 +335,25 @@ struct tracer_flags {
> #define TRACER_OPT(s, b) .name = #s, .bit = b
>
> /*
> + * If you want to provide a stat file (one-shot statistics), fill
> + * an iterator with stat_start/stat_next and a stat_show callbacks.
> + * The others callbacks are optional.
> + */
> +struct tracer_stat {
> + /* The name of your stat file */
> + const char *name;
> + /* Iteration over statistic entries */
> + void *(*stat_start)(void);
> + void *(*stat_next)(void *prev, int idx);
> + /* Compare two entries for sorting (optional) for stats */
> + int (*stat_cmp)(void *p1, void *p2);
> + /* Print a stat entry */
> + int (*stat_show)(struct seq_file *s, void *p);
> + /* Print the headers of your stat entries */
> + int (*stat_headers)(struct seq_file *s);
> +};
> +
> +/*
> * A specific tracer, represented by methods that operate on a trace array:
> */
> struct tracer {
> @@ -361,21 +380,7 @@ struct tracer {
> struct tracer *next;
> int print_max;
> struct tracer_flags *flags;
> -
> - /*
> - * If you change one of the following on tracing runtime, recall
> - * init_tracer_stat()
> - */
> -
> - /* Iteration over statistic entries */
> - void *(*stat_start)(void);
> - void *(*stat_next)(void *prev, int idx);
> - /* Compare two entries for sorting (optional) for stats */
> - int (*stat_cmp)(void *p1, void *p2);
> - /* Print a stat entry */
> - int (*stat_show)(struct seq_file *s, void *p);
> - /* Print the headers of your stat entries */
> - int (*stat_headers)(struct seq_file *s);
> + struct tracer_stat *stats;
> };
>
> struct trace_seq {
> diff --git a/kernel/trace/trace_stat.c b/kernel/trace/trace_stat.c
> index 6f194a3..293be1c 100644
> --- a/kernel/trace/trace_stat.c
> +++ b/kernel/trace/trace_stat.c
> @@ -21,31 +21,29 @@ struct trace_stat_list {
> void *stat;
> };
>
> -static struct trace_stat_list stat_list;
> +/* A stat session is the stats output in one file */
> +struct tracer_stat_session {
> + struct tracer_stat *ts;
> + struct trace_stat_list stat_list;
> + struct mutex stat_mutex;
> +};
>
> -/*
> - * 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;
> -
> -/*
> - * 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 *root = &session->stat_list;
> struct trace_stat_list *node;
> struct list_head *next;
>
> - if (list_empty(&stat_list.list))
> + if (list_empty(&root->list))
> return;
>
> - node = list_entry(stat_list.list.next, struct trace_stat_list, list);
> + node = list_entry(root->list.next, struct trace_stat_list, list);
> next = node->list.next;
>
> while (&node->list != next) {
> @@ -54,14 +52,65 @@ static void reset_stat_list(void)
> }
> kfree(node);
>
> - INIT_LIST_HEAD(&stat_list.list);
> + INIT_LIST_HEAD(&root->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)
> +{
> + int i, j;
> + struct tracer_stat_session *session;
> +
> + 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);
You want this to be kzalloc.
> + if (!all_stat_sessions)
> + return -ENOMEM;
> +
> + for (i = 0; i < nb; i++) {
> + session = kmalloc(sizeof(struct tracer_stat_session) * nb,
> + GFP_KERNEL);
Not so important, but you probably want to do it here too.
> + if (!session)
> + goto free_sessions;
> +
> + INIT_LIST_HEAD(&session->stat_list.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]);
With out the kzalloc above, this may crash the kernel, because
all_stat_sessions[i] might not be NULL when they were not initialized.
> +
> + kfree(all_stat_sessions);
> + all_stat_sessions = NULL;
> +
> + return -ENOMEM;
> +}
> +
> +static int basic_tracer_stat_checks(struct tracer_stat *ts)
> {
> - mutex_lock(&stat_list_mutex);
> - current_tracer = *trace;
> - mutex_unlock(&stat_list_mutex);
> + 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;
> }
>
> /*
> @@ -79,22 +128,19 @@ 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 trace_stat_list *iter_entry, *new_entry, *root;
> + 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
> @@ -107,8 +153,9 @@ static int stat_seq_init(void)
> }
>
> INIT_LIST_HEAD(&new_entry->list);
> - list_add(&new_entry->list, &stat_list.list);
> - new_entry->stat = current_tracer.stat_start();
> + root = &session->stat_list;
> + list_add(&new_entry->list, &root->list);
> + new_entry->stat = ts->stat_start();
>
> prev_stat = new_entry->stat;
>
> @@ -124,15 +171,15 @@ 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) {
> + list_for_each_entry(iter_entry, &root->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,
> @@ -141,7 +188,7 @@ static int stat_seq_init(void)
>
> /* The current smaller value */
> } else if (list_is_last(&iter_entry->list,
> - &stat_list.list)) {
> + &root->list)) {
> list_add(&new_entry->list, &iter_entry->list);
> break;
> }
> @@ -150,46 +197,49 @@ 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 trace_stat_list *l = (struct trace_stat_list *)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)
Hmm, looks like you do need the kzalloc for both allocs above.
-- Steve
> + session->ts->stat_headers(s);
>
> - return seq_list_start(&l->list, *pos);
> + return seq_list_start(&session->stat_list.list, *pos);
> }
>
> static void *stat_seq_next(struct seq_file *s, void *p, loff_t *pos)
> {
> - struct trace_stat_list *l = (struct trace_stat_list *)s->private;
> + struct tracer_stat_session *session = s->private;
>
> - return seq_list_next(p, &l->list, pos);
> + return seq_list_next(p, &session->stat_list.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 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, l->stat);
> +
> + return session->ts->stat_show(s, l->stat);
> }
>
> static const struct seq_operations trace_stat_seq_ops = {
> @@ -199,15 +249,18 @@ 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;
> @@ -219,9 +272,11 @@ 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;
> }
>
> @@ -232,18 +287,70 @@ 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;
>
> - INIT_LIST_HEAD(&stat_list.list);
> 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;
> --
> 1.6.0.4
>
>
>
>
--
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