Commit 4f271a2a authored by Vaibhav Nagarnaik's avatar Vaibhav Nagarnaik Committed by Steven Rostedt
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tracing: Add a proc file to stop tracing and free buffer 



The proc file entry buffer_size_kb is used to set the size of tracing
buffer. The memory to expand the buffer size is kernel memory. Consider
a use case where tracing is handled by a user space utility, which acts
as a gate keeper for tracing requests. In an OOM condition, tracing is
considered a low priority task and if the utility gets killed the ring
buffer memory cannot be released back to the kernel.

This patch adds a proc file called "free_buffer" whose purpose is to
stop tracing and free up the ring buffer when it is closed.

The user space process can then set the desired size in buffer_size_kb
file and open the fd to the "free_buffer" file. Under OOM condition, if
the process gets killed, the kernel closes the file descriptor. The
release handler stops the tracing and releases the kernel memory
automatically.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Michael Rubin <mrubin@google.com>
Cc: David Sharp <dhsharp@google.com>
Signed-off-by: default avatarVaibhav Nagarnaik <vnagarnaik@google.com>
Link: http://lkml.kernel.org/r/1308012717-11148-1-git-send-email-vnagarnaik@google.com


Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 7ea59064

kernel/trace/trace.c

+73 −35
Original line number Diff line number Diff line
@@ -2768,7 +2768,7 @@ int tracer_init(struct tracer *t, struct trace_array *tr) 
	return t->init(tr);

}



static int tracing_resize_ring_buffer(unsigned long size)

static int __tracing_resize_ring_buffer(unsigned long size)

{

	int ret;
@@ -2820,6 +2820,41 @@ static int tracing_resize_ring_buffer(unsigned long size) 
	return ret;

}



static ssize_t tracing_resize_ring_buffer(unsigned long size)

{

	int cpu, ret = size;



	mutex_lock(&trace_types_lock);



	tracing_stop();



	/* disable all cpu buffers */

	for_each_tracing_cpu(cpu) {

		if (global_trace.data[cpu])

			atomic_inc(&global_trace.data[cpu]->disabled);

		if (max_tr.data[cpu])

			atomic_inc(&max_tr.data[cpu]->disabled);

	}



	if (size != global_trace.entries)

		ret = __tracing_resize_ring_buffer(size);



	if (ret < 0)

		ret = -ENOMEM;



	for_each_tracing_cpu(cpu) {

		if (global_trace.data[cpu])

			atomic_dec(&global_trace.data[cpu]->disabled);

		if (max_tr.data[cpu])

			atomic_dec(&max_tr.data[cpu]->disabled);

	}



	tracing_start();

	mutex_unlock(&trace_types_lock);



	return ret;

}





/**

 * tracing_update_buffers - used by tracing facility to expand ring buffers
@@ -2837,7 +2872,7 @@ int tracing_update_buffers(void) 


	mutex_lock(&trace_types_lock);

	if (!ring_buffer_expanded)

		ret = tracing_resize_ring_buffer(trace_buf_size);

		ret = __tracing_resize_ring_buffer(trace_buf_size);

	mutex_unlock(&trace_types_lock);



	return ret;
@@ -2861,7 +2896,7 @@ static int tracing_set_tracer(const char *buf) 
	mutex_lock(&trace_types_lock);



	if (!ring_buffer_expanded) {

		ret = tracing_resize_ring_buffer(trace_buf_size);

		ret = __tracing_resize_ring_buffer(trace_buf_size);

		if (ret < 0)

			goto out;

		ret = 0;
@@ -3436,7 +3471,7 @@ tracing_entries_write(struct file *filp, const char __user *ubuf, 
{

	unsigned long val;

	char buf[64];

	int ret, cpu;

	int ret;



	if (cnt >= sizeof(buf))

		return -EINVAL;
@@ -3454,48 +3489,43 @@ tracing_entries_write(struct file *filp, const char __user *ubuf, 
	if (!val)

		return -EINVAL;



	mutex_lock(&trace_types_lock);



	tracing_stop();



	/* disable all cpu buffers */

	for_each_tracing_cpu(cpu) {

		if (global_trace.data[cpu])

			atomic_inc(&global_trace.data[cpu]->disabled);

		if (max_tr.data[cpu])

			atomic_inc(&max_tr.data[cpu]->disabled);

	}



	/* value is in KB */

	val <<= 10;



	if (val != global_trace.entries) {

	ret = tracing_resize_ring_buffer(val);

		if (ret < 0) {

			cnt = ret;

			goto out;

		}

	}

	if (ret < 0)

		return ret;



	*ppos += cnt;



	/* If check pages failed, return ENOMEM */

	if (tracing_disabled)

		cnt = -ENOMEM;

 out:

	for_each_tracing_cpu(cpu) {

		if (global_trace.data[cpu])

			atomic_dec(&global_trace.data[cpu]->disabled);

		if (max_tr.data[cpu])

			atomic_dec(&max_tr.data[cpu]->disabled);

	return cnt;

}



	tracing_start();

	mutex_unlock(&trace_types_lock);

static ssize_t

tracing_free_buffer_write(struct file *filp, const char __user *ubuf,

			  size_t cnt, loff_t *ppos)

{

	/*

	 * There is no need to read what the user has written, this function

	 * is just to make sure that there is no error when "echo" is used

	 */



	*ppos += cnt;



	return cnt;

}



static int

tracing_free_buffer_release(struct inode *inode, struct file *filp)

{

	/* disable tracing */

	tracing_off();

	/* resize the ring buffer to 0 */

	tracing_resize_ring_buffer(0);



	return 0;

}



static int mark_printk(const char *fmt, ...)

{

	int ret;
@@ -3641,6 +3671,11 @@ static const struct file_operations tracing_entries_fops = { 
	.llseek		= generic_file_llseek,

};



static const struct file_operations tracing_free_buffer_fops = {

	.write		= tracing_free_buffer_write,

	.release	= tracing_free_buffer_release,

};



static const struct file_operations tracing_mark_fops = {

	.open		= tracing_open_generic,

	.write		= tracing_mark_write,
@@ -4365,6 +4400,9 @@ static __init int tracer_init_debugfs(void) 
	trace_create_file("buffer_size_kb", 0644, d_tracer,

			&global_trace, &tracing_entries_fops);



	trace_create_file("free_buffer", 0644, d_tracer,

			&global_trace, &tracing_free_buffer_fops);



	trace_create_file("trace_marker", 0220, d_tracer,

			NULL, &tracing_mark_fops);

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