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

[Steven Rostedt]

From: Steven Rostedt <srostedt@xxxxxxxxxx>

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@xxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 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


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