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Date: Thu, 18 Jul 2013 12:31:27 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Alexander Z Lam <azl@...gle.com>
Cc: linux-kernel@...r.kernel.org, David Sharp <dhsharp@...gle.com>,
Vaibhav Nagarnaik <vnagarnaik@...gle.com>,
Alexander Z Lam <lambchop468@...il.com>,
Oleg Nesterov <oleg@...hat.com>,
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Subject: Re: [PATCH 1/2] tracing: Miscellaneous fixes for trace_array ref
counting
On Wed, 2013-07-10 at 17:34 -0700, Alexander Z Lam wrote:
> Some error paths did not handle ref counting properly, and some trace files need
> ref counting.
>
> Cc: Vaibhav Nagarnaik <vnagarnaik@...gle.com>
> Cc: David Sharp <dhsharp@...gle.com>
> Cc: Alexander Z Lam <lambchop468@...il.com>
> Signed-off-by: Alexander Z Lam <azl@...gle.com>
> ---
> kernel/trace/trace.c | 34 +++++++++++++++++++++++-----------
> kernel/trace/trace_events.c | 21 +++++++++++++++++++--
> 2 files changed, 42 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 0cd500b..ca2743b 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3008,7 +3008,6 @@ static int tracing_release(struct inode *inode, struct file *file)
>
> iter = m->private;
> tr = iter->tr;
> - trace_array_put(tr);
>
> mutex_lock(&trace_types_lock);
>
> @@ -3023,6 +3022,9 @@ static int tracing_release(struct inode *inode, struct file *file)
> if (!iter->snapshot)
> /* reenable tracing if it was previously enabled */
> tracing_start_tr(tr);
> +
> + __trace_array_put(tr);
> +
> mutex_unlock(&trace_types_lock);
>
> mutex_destroy(&iter->mutex);
> @@ -3447,6 +3449,7 @@ tracing_trace_options_write(struct file *filp, const char __user *ubuf,
> static int tracing_trace_options_open(struct inode *inode, struct file *file)
> {
> struct trace_array *tr = inode->i_private;
> + int ret;
>
> if (tracing_disabled)
> return -ENODEV;
> @@ -3454,7 +3457,11 @@ static int tracing_trace_options_open(struct inode *inode, struct file *file)
> if (trace_array_get(tr) < 0)
> return -ENODEV;
>
> - return single_open(file, tracing_trace_options_show, inode->i_private);
> + ret = single_open(file, tracing_trace_options_show, inode->i_private);
> + if (ret < 0)
> + trace_array_put(tr);
> +
> + return ret;
> }
>
> static const struct file_operations tracing_iter_fops = {
> @@ -3958,7 +3965,7 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)
> iter = kzalloc(sizeof(*iter), GFP_KERNEL);
> if (!iter) {
> ret = -ENOMEM;
> - goto out;
> + goto fail_iter;
It would be cleaner to not add the extra label, and just do a
trace_array_put() in the if statement.
> }
>
> /*
> @@ -3968,13 +3975,13 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)
> iter->trace = kmalloc(sizeof(*iter->trace), GFP_KERNEL);
> if (!iter->trace) {
> ret = -ENOMEM;
> - goto fail;
> + goto fail_trace;
> }
> *iter->trace = *tr->current_trace;
>
> if (!alloc_cpumask_var(&iter->started, GFP_KERNEL)) {
> ret = -ENOMEM;
> - goto fail;
> + goto fail_trace;
> }
>
> /* trace pipe does not show start of buffer */
> @@ -4001,9 +4008,10 @@ out:
> mutex_unlock(&trace_types_lock);
> return ret;
>
> -fail:
> +fail_trace:
> kfree(iter->trace);
> kfree(iter);
> +fail_iter:
> __trace_array_put(tr);
> mutex_unlock(&trace_types_lock);
> return ret;
> @@ -4705,12 +4713,15 @@ static int tracing_snapshot_open(struct inode *inode, struct file *file)
> } else {
> /* Writes still need the seq_file to hold the private data */
> m = kzalloc(sizeof(*m), GFP_KERNEL);
> - if (!m)
> - return -ENOMEM;
> + if (!m) {
> + ret = -ENOMEM;
> + goto out;
> + }
Instead of adding the complex if statement, do this:
int ret = -ENOMEM;
[..]
if (!m)
goto out;
And then after the if statements:
ret = 0;
> iter = kzalloc(sizeof(*iter), GFP_KERNEL);
> if (!iter) {
> kfree(m);
> - return -ENOMEM;
> + ret = -ENOMEM;
> + goto out;
> }
> iter->tr = tr;
> iter->trace_buffer = &tc->tr->max_buffer;
> @@ -4718,7 +4729,7 @@ static int tracing_snapshot_open(struct inode *inode, struct file *file)
> m->private = iter;
> file->private_data = m;
> }
> -
> +out:
> if (ret < 0)
> trace_array_put(tr);
>
The rest looks good. Although, we may be rewriting all this code because
there still exists some races. See the email threads between Oleg and
Masami.
-- Steve
> @@ -5328,9 +5339,10 @@ tracing_stats_read(struct file *filp, char __user *ubuf,
> }
>
> static const struct file_operations tracing_stats_fops = {
> - .open = tracing_open_generic,
> + .open = tracing_open_generic_tc,
> .read = tracing_stats_read,
> .llseek = generic_file_llseek,
> + .release = tracing_release_generic_tc,
> };
>
> #ifdef CONFIG_DYNAMIC_FTRACE
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 7d85429..7a75cb2 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -1218,6 +1218,7 @@ show_header(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
>
> 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_release(struct inode *inode, struct file *file);
>
> static const struct seq_operations show_event_seq_ops = {
> .start = t_start,
> @@ -1245,7 +1246,7 @@ static const struct file_operations ftrace_set_event_fops = {
> .read = seq_read,
> .write = ftrace_event_write,
> .llseek = seq_lseek,
> - .release = seq_release,
> + .release = ftrace_event_release,
> };
>
> static const struct file_operations ftrace_enable_fops = {
> @@ -1323,6 +1324,15 @@ ftrace_event_open(struct inode *inode, struct file *file,
> return ret;
> }
>
> +static int ftrace_event_release(struct inode *inode, struct file *file)
> +{
> + struct trace_array *tr = inode->i_private;
> +
> + trace_array_put(tr);
> +
> + return seq_release(inode, file);
> +}
> +
> static int
> ftrace_event_avail_open(struct inode *inode, struct file *file)
> {
> @@ -1336,12 +1346,19 @@ ftrace_event_set_open(struct inode *inode, struct file *file)
> {
> const struct seq_operations *seq_ops = &show_set_event_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_events(tr);
>
> - return ftrace_event_open(inode, file, seq_ops);
> + ret = ftrace_event_open(inode, file, seq_ops);
> + if (ret < 0)
> + trace_array_put(tr);
> + return ret;
> }
>
> static struct event_subsystem *
--
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