2 files changed, 57 insertions, 8 deletions

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index d8bae6f4219e..e2a4ff6fc3a6 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -244,10 +244,15 @@ config STACK_TRACER
 
           This tracer works by hooking into every function call that the
           kernel executes, and keeping a maximum stack depth value and
-          stack-trace saved. Because this logic has to execute in every
-          kernel function, all the time, this option can slow down the
-          kernel measurably and is generally intended for kernel
-          developers only.
+          stack-trace saved.  If this is configured with DYNAMIC_FTRACE
+          then it will not have any overhead while the stack tracer
+          is disabled.
+
+          To enable the stack tracer on bootup, pass in 'stacktrace'
+          on the kernel command line.
+
+          The stack tracer can also be enabled or disabled via the
+          sysctl kernel.stack_tracer_enabled
 
           Say N if unsure.
 
diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 0b863f2cbc8e..4842c969c785 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -10,6 +10,7 @@
 #include <linux/debugfs.h>
 #include <linux/ftrace.h>
 #include <linux/module.h>
+#include <linux/sysctl.h>
 #include <linux/init.h>
 #include <linux/fs.h>
 #include "trace.h"
@@ -31,6 +32,10 @@ static raw_spinlock_t max_stack_lock =
 
 static int stack_trace_disabled __read_mostly;
 static DEFINE_PER_CPU(int, trace_active);
+static DEFINE_MUTEX(stack_sysctl_mutex);
+
+int stack_tracer_enabled;
+static int last_stack_tracer_enabled;
 
 static inline void check_stack(void)
 {
@@ -174,7 +179,7 @@ stack_max_size_write(struct file *filp, const char __user *ubuf,
         return count;
 }
 
-static struct file_operations stack_max_size_fops = {
+static const struct file_operations stack_max_size_fops = {
         .open           = tracing_open_generic,
         .read           = stack_max_size_read,
         .write          = stack_max_size_write,
@@ -272,7 +277,7 @@ static int t_show(struct seq_file *m, void *v)
         return 0;
 }
 
-static struct seq_operations stack_trace_seq_ops = {
+static const struct seq_operations stack_trace_seq_ops = {
         .start          = t_start,
         .next           = t_next,
         .stop           = t_stop,
@@ -288,12 +293,48 @@ static int stack_trace_open(struct inode *inode, struct file *file)
         return ret;
 }
 
-static struct file_operations stack_trace_fops = {
+static const struct file_operations stack_trace_fops = {
         .open           = stack_trace_open,
         .read           = seq_read,
         .llseek         = seq_lseek,
 };
 
+int
+stack_trace_sysctl(struct ctl_table *table, int write,
+                   struct file *file, void __user *buffer, size_t *lenp,
+                   loff_t *ppos)
+{
+        int ret;
+
+        mutex_lock(&stack_sysctl_mutex);
+
+        ret  = proc_dointvec(table, write, file, buffer, lenp, ppos);
+
+        if (ret || !write ||
+            (last_stack_tracer_enabled == stack_tracer_enabled))
+                goto out;
+
+        last_stack_tracer_enabled = stack_tracer_enabled;
+
+        if (stack_tracer_enabled)
+                register_ftrace_function(&trace_ops);
+        else
+                unregister_ftrace_function(&trace_ops);
+
+ out:
+        mutex_unlock(&stack_sysctl_mutex);
+        return ret;
+}
+
+static int start_stack_trace __initdata;
+
+static __init int enable_stacktrace(char *str)
+{
+        start_stack_trace = 1;
+        return 1;
+}
+__setup("stacktrace", enable_stacktrace);
+
 static __init int stack_trace_init(void)
 {
         struct dentry *d_tracer;
@@ -311,7 +352,10 @@ static __init int stack_trace_init(void)
         if (!entry)
                 pr_warning("Could not create debugfs 'stack_trace' entry\n");
 
-        register_ftrace_function(&trace_ops);
+        if (start_stack_trace) {
+                register_ftrace_function(&trace_ops);
+                stack_tracer_enabled = 1;
+        }
 
         return 0;
 }