[PATCH 20/21] tracing: Do not allocate buffer for trace_marker

Steven Rostedt
2011-09-22T22:10:50Z

[-- Attachment #1: 0020-tracing-Do-not-allocate-buffer-for-trace_marker.patch --]
[-- Type: text/plain, Size: 3191 bytes --]

From: Steven Rostedt <srostedt@redhat.com>

When doing intense tracing, the kmalloc inside trace_marker can
introduce side effects to what is being traced. It is best to simply
use a static buffer and grab a mutex to write to it. This keeps
the impact of using the trace_marker() to a minimum.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/trace/trace.c | 33 +++++++++++++++++----------------
1 files changed, 17 insertions(+), 16 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4b8df0d..e463125 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1442,15 +1442,19 @@ static void __trace_userstack(struct trace_array *tr, unsigned long flags)

#endif /* CONFIG_STACKTRACE */

+static char trace_buf[TRACE_BUF_SIZE];
+static char trace_ubuf[TRACE_BUF_SIZE];
+
+static arch_spinlock_t trace_buf_lock =
+ (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
+static DEFINE_MUTEX(trace_ubuf_mutex);
+
/**
* trace_vbprintk - write binary msg to tracing buffer
*
*/
int trace_vbprintk(unsigned long ip, const char *fmt, va_list args)
{
- static arch_spinlock_t trace_buf_lock =
- (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
- static u32 trace_buf[TRACE_BUF_SIZE];

struct ftrace_event_call *call = &event_bprint;
struct ring_buffer_event *event;
@@ -1480,7 +1484,7 @@ int trace_vbprintk(unsigned long ip, const char *fmt, va_list args)
/* Lockdep uses trace_printk for lock tracing */
local_irq_save(flags);
arch_spin_lock(&trace_buf_lock);
- len = vbin_printf(trace_buf, TRACE_BUF_SIZE, fmt, args);
+ len = vbin_printf((u32 *)trace_buf, TRACE_BUF_SIZE/sizeof(int), fmt, args);

if (len > TRACE_BUF_SIZE || len < 0)
goto out_unlock;
@@ -1532,9 +1536,6 @@ int trace_array_printk(struct trace_array *tr,
int trace_array_vprintk(struct trace_array *tr,
unsigned long ip, const char *fmt, va_list args)
{
- static arch_spinlock_t trace_buf_lock = __ARCH_SPIN_LOCK_UNLOCKED;
- static char trace_buf[TRACE_BUF_SIZE];
-
struct ftrace_event_call *call = &event_print;
struct ring_buffer_event *event;
struct ring_buffer *buffer;
@@ -3633,23 +3634,22 @@ static ssize_t
tracing_mark_write(struct file *filp, const char __user *ubuf,
size_t cnt, loff_t *fpos)
{
- char *buf;
size_t written;
+ char *buf = trace_ubuf;

if (tracing_disabled)
return -EINVAL;

- if (cnt > TRACE_BUF_SIZE)
- cnt = TRACE_BUF_SIZE;
+ if (cnt >= TRACE_BUF_SIZE)
+ cnt = TRACE_BUF_SIZE - 2; /* \n\0 */

- buf = kmalloc(cnt + 2, GFP_KERNEL);
- if (buf == NULL)
- return -ENOMEM;
+ mutex_lock(&trace_ubuf_mutex);

if (copy_from_user(buf, ubuf, cnt)) {
- kfree(buf);
- return -EFAULT;
+ written = -EFAULT;
+ goto out;
}
+
if (buf[cnt-1] != '\n') {
buf[cnt] = '\n';
buf[cnt+1] = '\0';
@@ -3657,12 +3657,13 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
buf[cnt] = '\0';

written = mark_printk("%s", buf);
- kfree(buf);
*fpos += written;

/* don't tell userspace we wrote more - it might confuse them */
if (written > cnt)
written = cnt;
+ out:
+ mutex_unlock(&trace_ubuf_mutex);

return written;
}
--
1.7.5.4