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tracing: Add a proc file to stop tracing and free buffer

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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: Vaibhav Nagarnaik <vnagarnaik@google.com>
Link: http://lkml.kernel.org/r/1308012717-11148-1-git-send-email-vnagarnaik@google.com
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Vaibhav Nagarnaik 2011-06-13 17:51:57 -07:00 committed by Steven Rostedt
parent 7ea5906405
commit 4f271a2a60
1 changed files with 73 additions and 35 deletions
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108
kernel/trace/trace.c
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@ -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;
}
}
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;
@ -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);