3 files changed, 38 insertions, 3 deletions

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index a3d46151be19..9623b7b9e5a5 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -165,6 +165,8 @@ static inline void __ftrace_enabled_restore(int enabled)
 #endif
 
 #ifdef CONFIG_TRACING
+extern int ftrace_dump_on_oops;
+
 extern void
 ftrace_special(unsigned long arg1, unsigned long arg2, unsigned long arg3);
 
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index a13bd4dfaeb1..84754f5801e6 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -484,6 +484,16 @@ static struct ctl_table kern_table[] = {
                 .proc_handler   = &ftrace_enable_sysctl,
         },
 #endif
+#ifdef CONFIG_TRACING
+        {
+                .ctl_name       = CTL_UNNUMBERED,
+                .procname       = "ftrace_dump_on_opps",
+                .data           = &ftrace_dump_on_oops,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec,
+        },
+#endif
 #ifdef CONFIG_MODULES
         {
                 .ctl_name       = KERN_MODPROBE,
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d345d649d073..47f46cbdd860 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -63,6 +63,28 @@ static cpumask_t __read_mostly		tracing_buffer_mask;
 
 static int tracing_disabled = 1;
 
+/*
+ * ftrace_dump_on_oops - variable to dump ftrace buffer on oops
+ *
+ * If there is an oops (or kernel panic) and the ftrace_dump_on_oops
+ * is set, then ftrace_dump is called. This will output the contents
+ * of the ftrace buffers to the console.  This is very useful for
+ * capturing traces that lead to crashes and outputing it to a
+ * serial console.
+ *
+ * It is default off, but you can enable it with either specifying
+ * "ftrace_dump_on_oops" in the kernel command line, or setting
+ * /proc/sys/kernel/ftrace_dump_on_oops to true.
+ */
+int ftrace_dump_on_oops;
+
+static int __init set_ftrace_dump_on_oops(char *str)
+{
+        ftrace_dump_on_oops = 1;
+        return 1;
+}
+__setup("ftrace_dump_on_oops", set_ftrace_dump_on_oops);
+
 long
 ns2usecs(cycle_t nsec)
 {
@@ -3021,7 +3043,8 @@ EXPORT_SYMBOL_GPL(__ftrace_printk);
 static int trace_panic_handler(struct notifier_block *this,
                                unsigned long event, void *unused)
 {
-        ftrace_dump();
+        if (ftrace_dump_on_oops)
+                ftrace_dump();
         return NOTIFY_OK;
 }
 
@@ -3037,7 +3060,8 @@ static int trace_die_handler(struct notifier_block *self,
 {
         switch (val) {
         case DIE_OOPS:
-                ftrace_dump();
+                if (ftrace_dump_on_oops)
+                        ftrace_dump();
                 break;
         default:
                 break;
@@ -3078,7 +3102,6 @@ trace_printk_seq(struct trace_seq *s)
         trace_seq_reset(s);
 }
 
-
 void ftrace_dump(void)
 {
         static DEFINE_SPINLOCK(ftrace_dump_lock);