---

yaml
---
r: 140795
b: refs/heads/master
c: d7350c3
h: refs/heads/master
i:
  140793: 418d5ba
  140791: f44b2a0
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: b04cc6b1f6398b0e0b60d37e27ce51b4899672ec
+refs/heads/master: d7350c3f45694104e820041969c8185c5f99e57c

trunk/kernel/trace/trace.c

@@ -1294,20 +1294,32 @@ static void *s_next(struct seq_file *m, void *v, loff_t *pos)
 	return ent;
 }
 
+/*
+ * No necessary locking here. The worst thing which can
+ * happen is loosing events consumed at the same time
+ * by a trace_pipe reader.
+ * Other than that, we don't risk to crash the ring buffer
+ * because it serializes the readers.
+ *
+ * The current tracer is copied to avoid a global locking
+ * all around.
+ */
 static void *s_start(struct seq_file *m, loff_t *pos)
 {
 	struct trace_iterator *iter = m->private;
+	static struct tracer *old_tracer;
 	int cpu_file = iter->cpu_file;
 	void *p = NULL;
 	loff_t l = 0;
 	int cpu;
 
+	/* copy the tracer to avoid using a global lock all around */
 	mutex_lock(&trace_types_lock);
-
-	if (!current_trace || current_trace != iter->trace) {
-		mutex_unlock(&trace_types_lock);
-		return NULL;
+	if (unlikely(old_tracer != current_trace && current_trace)) {
+		old_tracer = current_trace;
+		*iter->trace = *current_trace;
 	}
+	mutex_unlock(&trace_types_lock);
 
 	atomic_inc(&trace_record_cmdline_disabled);
 
@@ -1341,7 +1353,6 @@ static void *s_start(struct seq_file *m, loff_t *pos)
 static void s_stop(struct seq_file *m, void *p)
 {
 	atomic_dec(&trace_record_cmdline_disabled);
-	mutex_unlock(&trace_types_lock);
 }
 
 static void print_lat_help_header(struct seq_file *m)
@@ -1691,13 +1702,25 @@ __tracing_open(struct inode *inode, struct file *file, int *ret)
 		goto out;
 	}
 
+	/*
+	 * We make a copy of the current tracer to avoid concurrent
+	 * changes on it while we are reading.
+	 */
 	mutex_lock(&trace_types_lock);
+	iter->trace = kzalloc(sizeof(*iter->trace), GFP_KERNEL);
+	if (!iter->trace) {
+		*ret = -ENOMEM;
+		goto fail;
+	}
+	if (current_trace)
+		*iter->trace = *current_trace;
+
 	if (current_trace && current_trace->print_max)
 		iter->tr = &max_tr;
 	else
 		iter->tr = &global_trace;
-	iter->trace = current_trace;
 	iter->pos = -1;
+	mutex_init(&iter->mutex);
 	iter->cpu_file = cpu_file;
 
 	/* Notify the tracer early; before we stop tracing. */
@@ -1747,8 +1770,9 @@ __tracing_open(struct inode *inode, struct file *file, int *ret)
 		if (iter->buffer_iter[cpu])
 			ring_buffer_read_finish(iter->buffer_iter[cpu]);
 	}
-fail:
+ fail:
 	mutex_unlock(&trace_types_lock);
+	kfree(iter->trace);
 	kfree(iter);
 
 	return ERR_PTR(-ENOMEM);
@@ -1783,6 +1807,8 @@ static int tracing_release(struct inode *inode, struct file *file)
 	mutex_unlock(&trace_types_lock);
 
 	seq_release(inode, file);
+	mutex_destroy(&iter->mutex);
+	kfree(iter->trace);
 	kfree(iter);
 	return 0;
 }
@@ -2392,18 +2418,29 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)
 		goto out;
 	}
 
+	/*
+	 * We make a copy of the current tracer to avoid concurrent
+	 * changes on it while we are reading.
+	 */
+	iter->trace = kmalloc(sizeof(*iter->trace), GFP_KERNEL);
+	if (!iter->trace) {
+		ret = -ENOMEM;
+		goto fail;
+	}
+	if (current_trace)
+		*iter->trace = *current_trace;
+
 	if (!alloc_cpumask_var(&iter->started, GFP_KERNEL)) {
-		kfree(iter);
 		ret = -ENOMEM;
-		goto out;
+		goto fail;
 	}
 
 	/* trace pipe does not show start of buffer */
 	cpumask_setall(iter->started);
 
 	iter->cpu_file = cpu_file;
 	iter->tr = &global_trace;
-	iter->trace = current_trace;
+	mutex_init(&iter->mutex);
 	filp->private_data = iter;
 
 	if (iter->trace->pipe_open)
@@ -2412,6 +2449,12 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)
 out:
 	mutex_unlock(&trace_types_lock);
 	return ret;
+
+fail:
+	kfree(iter->trace);
+	kfree(iter);
+	mutex_unlock(&trace_types_lock);
+	return ret;
 }
 
 static int tracing_release_pipe(struct inode *inode, struct file *file)
@@ -2428,6 +2471,8 @@ static int tracing_release_pipe(struct inode *inode, struct file *file)
 	mutex_unlock(&trace_types_lock);
 
 	free_cpumask_var(iter->started);
+	mutex_destroy(&iter->mutex);
+	kfree(iter->trace);
 	kfree(iter);
 
 	return 0;
@@ -2497,18 +2542,15 @@ static int tracing_wait_pipe(struct file *filp)
 			return -EAGAIN;
 		}
 
-		mutex_unlock(&trace_types_lock);
+		mutex_unlock(&iter->mutex);
 
 		iter->trace->wait_pipe(iter);
 
-		mutex_lock(&trace_types_lock);
+		mutex_lock(&iter->mutex);
 
 		if (signal_pending(current))
 			return -EINTR;
 
-		if (iter->trace != current_trace)
-			return 0;
-
 		/*
 		 * We block until we read something and tracing is disabled.
 		 * We still block if tracing is disabled, but we have never
@@ -2533,6 +2575,7 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 		  size_t cnt, loff_t *ppos)
 {
 	struct trace_iterator *iter = filp->private_data;
+	static struct tracer *old_tracer;
 	ssize_t sret;
 
 	/* return any leftover data */
@@ -2542,7 +2585,20 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 
 	trace_seq_reset(&iter->seq);
 
+	/* copy the tracer to avoid using a global lock all around */
 	mutex_lock(&trace_types_lock);
+	if (unlikely(old_tracer != current_trace && current_trace)) {
+		old_tracer = current_trace;
+		*iter->trace = *current_trace;
+	}
+	mutex_unlock(&trace_types_lock);
+
+	/*
+	 * Avoid more than one consumer on a single file descriptor
+	 * This is just a matter of traces coherency, the ring buffer itself
+	 * is protected.
+	 */
+	mutex_lock(&iter->mutex);
 	if (iter->trace->read) {
 		sret = iter->trace->read(iter, filp, ubuf, cnt, ppos);
 		if (sret)
@@ -2599,7 +2655,7 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 		goto waitagain;
 
 out:
-	mutex_unlock(&trace_types_lock);
+	mutex_unlock(&iter->mutex);
 
 	return sret;
 }
@@ -2676,11 +2732,20 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
 		.ops		= &tracing_pipe_buf_ops,
 		.spd_release	= tracing_spd_release_pipe,
 	};
+	static struct tracer *old_tracer;
 	ssize_t ret;
 	size_t rem;
 	unsigned int i;
 
+	/* copy the tracer to avoid using a global lock all around */
 	mutex_lock(&trace_types_lock);
+	if (unlikely(old_tracer != current_trace && current_trace)) {
+		old_tracer = current_trace;
+		*iter->trace = *current_trace;
+	}
+	mutex_unlock(&trace_types_lock);
+
+	mutex_lock(&iter->mutex);
 
 	if (iter->trace->splice_read) {
 		ret = iter->trace->splice_read(iter, filp,
@@ -2720,14 +2785,14 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
 		trace_seq_reset(&iter->seq);
 	}
 
-	mutex_unlock(&trace_types_lock);
+	mutex_unlock(&iter->mutex);
 
 	spd.nr_pages = i;
 
 	return splice_to_pipe(pipe, &spd);
 
 out_err:
-	mutex_unlock(&trace_types_lock);
+	mutex_unlock(&iter->mutex);
 
 	return ret;
 }

trunk/kernel/trace/trace.h

@@ -405,8 +405,9 @@ struct trace_iterator {
 	struct trace_array	*tr;
 	struct tracer		*trace;
 	void			*private;
-	struct ring_buffer_iter	*buffer_iter[NR_CPUS];
 	int			cpu_file;
+	struct mutex		mutex;
+	struct ring_buffer_iter	*buffer_iter[NR_CPUS];
 
 	/* The below is zeroed out in pipe_read */
 	struct trace_seq	seq;