5 files changed, 79 insertions, 8 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 2919a2e91938..edab81c13182 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -89,6 +89,7 @@ parameter is applicable:
         SPARC   Sparc architecture is enabled.
         SWSUSP  Software suspend (hibernation) is enabled.
         SUSPEND System suspend states are enabled.
+        FTRACE  Function tracing enabled.
         TS      Appropriate touchscreen support is enabled.
         USB     USB support is enabled.
         USBHID  USB Human Interface Device support is enabled.
@@ -2173,6 +2174,9 @@ and is between 256 and 4096 characters. It is defined in the file
         st=             [HW,SCSI] SCSI tape parameters (buffers, etc.)
                         See Documentation/scsi/st.txt.
 
+        stacktrace      [FTRACE]
+                        Enabled the stack tracer on boot up.
+
         sti=            [PARISC,HW]
                         Format: <num>
                         Set the STI (builtin display/keyboard on the HP-PARISC
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 44020f31bd81..6b0db53caa7d 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -86,6 +86,14 @@ static inline void ftrace_stop(void) { }
 static inline void ftrace_start(void) { }
 #endif /* CONFIG_FUNCTION_TRACER */
 
+#ifdef CONFIG_STACK_TRACER
+extern int stack_tracer_enabled;
+int
+stack_trace_sysctl(struct ctl_table *table, int write,
+                   struct file *file, void __user *buffer, size_t *lenp,
+                   loff_t *ppos);
+#endif
+
 #ifdef CONFIG_DYNAMIC_FTRACE
 /* asm/ftrace.h must be defined for archs supporting dynamic ftrace */
 #include <asm/ftrace.h>
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index c83f566e940a..6ac501a2dcc6 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -487,6 +487,16 @@ static struct ctl_table kern_table[] = {
                 .proc_handler   = &ftrace_enable_sysctl,
         },
 #endif
+#ifdef CONFIG_STACK_TRACER
+        {
+                .ctl_name       = CTL_UNNUMBERED,
+                .procname       = "stack_tracer_enabled",
+                .data           = &stack_tracer_enabled,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = &stack_trace_sysctl,
+        },
+#endif
 #ifdef CONFIG_TRACING
         {
                 .ctl_name       = CTL_UNNUMBERED,
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;
 }