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Date: Mon, 01 Jul 2013 22:37:33 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Alexander Lam <azl@...gle.com>
Cc: linux-kernel@...r.kernel.org, David Sharp <dhsharp@...gle.com>,
Vaibhav Nagarnaik <vnagarnaik@...gle.com>,
Alexander Lam <lambchop468@...il.com>
Subject: Re: Fwd: [draft] Tracing multibuffer support concurrency issues
On Mon, 2013-07-01 at 21:35 -0400, Steven Rostedt wrote:
> >
> > Is there a better way to fix this problem?
> >
> > Also unaddressed are all of the other files which use a trace_array,
> > trace_cpu, or ftrace_event_file in their operation - these would need
> > the same fix.
>
> Hmm, really? Just the initiator. That is, when an event is enabled or
> anything gets opened, we block deletion from happening. That way we
> don't need to care about the rest. Only open and enabling events.
I added two helper functions to handle this. trace_array_get() and
trace_array_put(). This patch prevents your example from crashing.
This probably needs to be added to opening of other files if not already
done.
-- Steve
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index e36da7f..89a3930 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -204,6 +204,37 @@ static struct trace_array global_trace;
LIST_HEAD(ftrace_trace_arrays);
+int trace_array_get(struct trace_array *this_tr)
+{
+ struct trace_array *tr;
+ int ret = -ENODEV;
+
+ mutex_lock(&trace_types_lock);
+ list_for_each_entry(tr, &ftrace_trace_arrays, list) {
+ if (tr == this_tr) {
+ tr->ref++;
+ ret = 0;
+ break;
+ }
+ }
+ mutex_unlock(&trace_types_lock);
+
+ return ret;
+}
+
+static void __trace_array_put(struct trace_array *this_tr)
+{
+ WARN_ON(!this_tr->ref);
+ this_tr->ref--;
+}
+
+void trace_array_put(struct trace_array *this_tr)
+{
+ mutex_lock(&trace_types_lock);
+ __trace_array_put(this_tr);
+ mutex_unlock(&trace_types_lock);
+}
+
int filter_current_check_discard(struct ring_buffer *buffer,
struct ftrace_event_call *call, void *rec,
struct ring_buffer_event *event)
@@ -2831,10 +2862,9 @@ static const struct seq_operations tracer_seq_ops = {
};
static struct trace_iterator *
-__tracing_open(struct inode *inode, struct file *file, bool snapshot)
+__tracing_open(struct trace_array *tr, struct trace_cpu *tc,
+ struct inode *inode, struct file *file, bool snapshot)
{
- struct trace_cpu *tc = inode->i_private;
- struct trace_array *tr = tc->tr;
struct trace_iterator *iter;
int cpu;
@@ -2913,8 +2943,6 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot)
tracing_iter_reset(iter, cpu);
}
- tr->ref++;
-
mutex_unlock(&trace_types_lock);
return iter;
@@ -2944,17 +2972,20 @@ static int tracing_release(struct inode *inode, struct file *file)
struct trace_array *tr;
int cpu;
- if (!(file->f_mode & FMODE_READ))
+ /* Writes do not use seq_file, need to grab tr from inode */
+ if (!(file->f_mode & FMODE_READ)) {
+ struct trace_cpu *tc = inode->i_private;
+
+ trace_array_put(tc->tr);
return 0;
+ }
iter = m->private;
tr = iter->tr;
+ trace_array_put(tr);
mutex_lock(&trace_types_lock);
- WARN_ON(!tr->ref);
- tr->ref--;
-
for_each_tracing_cpu(cpu) {
if (iter->buffer_iter[cpu])
ring_buffer_read_finish(iter->buffer_iter[cpu]);
@@ -2973,20 +3004,23 @@ static int tracing_release(struct inode *inode, struct file *file)
kfree(iter->trace);
kfree(iter->buffer_iter);
seq_release_private(inode, file);
+
return 0;
}
static int tracing_open(struct inode *inode, struct file *file)
{
+ struct trace_cpu *tc = inode->i_private;
+ struct trace_array *tr = tc->tr;
struct trace_iterator *iter;
int ret = 0;
+ if (trace_array_get(tr) < 0)
+ return -ENODEV;
+
/* If this file was open for write, then erase contents */
if ((file->f_mode & FMODE_WRITE) &&
(file->f_flags & O_TRUNC)) {
- struct trace_cpu *tc = inode->i_private;
- struct trace_array *tr = tc->tr;
-
if (tc->cpu == RING_BUFFER_ALL_CPUS)
tracing_reset_online_cpus(&tr->trace_buffer);
else
@@ -2994,12 +3028,16 @@ static int tracing_open(struct inode *inode, struct file *file)
}
if (file->f_mode & FMODE_READ) {
- iter = __tracing_open(inode, file, false);
+ iter = __tracing_open(tr, tc, inode, file, false);
if (IS_ERR(iter))
ret = PTR_ERR(iter);
else if (trace_flags & TRACE_ITER_LATENCY_FMT)
iter->iter_flags |= TRACE_FILE_LAT_FMT;
}
+
+ if (ret < 0)
+ trace_array_put(tr);
+
return ret;
}
@@ -4575,12 +4613,16 @@ struct ftrace_buffer_info {
static int tracing_snapshot_open(struct inode *inode, struct file *file)
{
struct trace_cpu *tc = inode->i_private;
+ struct trace_array *tr = tc->tr;
struct trace_iterator *iter;
struct seq_file *m;
int ret = 0;
+ if (trace_array_get(tr) < 0)
+ return -ENODEV;
+
if (file->f_mode & FMODE_READ) {
- iter = __tracing_open(inode, file, true);
+ iter = __tracing_open(tr, tc, inode, file, true);
if (IS_ERR(iter))
ret = PTR_ERR(iter);
} else {
@@ -4593,13 +4635,16 @@ static int tracing_snapshot_open(struct inode *inode, struct file *file)
kfree(m);
return -ENOMEM;
}
- iter->tr = tc->tr;
+ iter->tr = tr;
iter->trace_buffer = &tc->tr->max_buffer;
iter->cpu_file = tc->cpu;
m->private = iter;
file->private_data = m;
}
+ if (ret < 0)
+ trace_array_put(tr);
+
return ret;
}
@@ -4680,9 +4725,12 @@ out:
static int tracing_snapshot_release(struct inode *inode, struct file *file)
{
struct seq_file *m = file->private_data;
+ int ret;
+
+ ret = tracing_release(inode, file);
if (file->f_mode & FMODE_READ)
- return tracing_release(inode, file);
+ return ret;
/* If write only, the seq_file is just a stub */
if (m)
@@ -4927,8 +4975,7 @@ static int tracing_buffers_release(struct inode *inode, struct file *file)
mutex_lock(&trace_types_lock);
- WARN_ON(!iter->tr->ref);
- iter->tr->ref--;
+ trace_array_put(iter->tr);
if (info->spare)
ring_buffer_free_read_page(iter->trace_buffer->buffer, info->spare);
--
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