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Date: Mon, 13 Jun 2011 17:51:57 -0700
From: Vaibhav Nagarnaik <vnagarnaik@...gle.com>
To: Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>,
Frederic Weisbecker <fweisbec@...il.com>
Cc: Michael Rubin <mrubin@...gle.com>,
David Sharp <dhsharp@...gle.com>, linux-kernel@...r.kernel.org,
Vaibhav Nagarnaik <vnagarnaik@...gle.com>
Subject: [PATCH v2] trace: 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.
Signed-off-by: Vaibhav Nagarnaik <vnagarnaik@...gle.com>
---
Changelog:
v2-v1:
* Change name of file from "free_ring_buffer" to "free_buffer"
kernel/trace/trace.c | 108 +++++++++++++++++++++++++++++++++----------------
1 files changed, 73 insertions(+), 35 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ee9c921..7c19a07 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2767,7 +2767,7 @@ 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;
@@ -2819,6 +2819,41 @@ 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
@@ -2836,7 +2871,7 @@ 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;
@@ -2860,7 +2895,7 @@ 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;
@@ -3435,7 +3470,7 @@ 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;
@@ -3453,48 +3488,43 @@ 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;
- }
- }
+ ret = tracing_resize_ring_buffer(val);
+ 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;
@@ -3640,6 +3670,11 @@ 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);
--
1.7.3.1
--
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