kernel/sysctl: add panic_print into sysctl

So that we can also runtime chose to print out the needed system info
for panic, other than setting the kernel cmdline.

Link: http://lkml.kernel.org/r/1543398842-19295-3-git-send-email-feng.tang@intel.com
Signed-off-by: Feng Tang <feng.tang@intel.com>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/panic.c b/kernel/panic.c
index 855f667..f121e6b 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -51,7 +51,7 @@
 #define PANIC_PRINT_TIMER_INFO		0x00000004
 #define PANIC_PRINT_LOCK_INFO		0x00000008
 #define PANIC_PRINT_FTRACE_INFO		0x00000010
-static unsigned long panic_print;
+unsigned long panic_print;
 
 ATOMIC_NOTIFIER_HEAD(panic_notifier_list);
 
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 7f6c1a3..ba4d9e8 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -807,6 +807,13 @@
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
+	{
+		.procname	= "panic_print",
+		.data		= &panic_print,
+		.maxlen		= sizeof(unsigned long),
+		.mode		= 0644,
+		.proc_handler	= proc_doulongvec_minmax,
+	},
 #if defined CONFIG_PRINTK
 	{
 		.procname	= "printk",
diff --git a/kernel/sysctl_binary.c b/kernel/sysctl_binary.c
index 07148b4..73c1320 100644
--- a/kernel/sysctl_binary.c
+++ b/kernel/sysctl_binary.c
@@ -140,6 +140,7 @@
 	{ CTL_INT,	KERN_MAX_LOCK_DEPTH,		"max_lock_depth" },
 	{ CTL_INT,	KERN_PANIC_ON_NMI,		"panic_on_unrecovered_nmi" },
 	{ CTL_INT,	KERN_PANIC_ON_WARN,		"panic_on_warn" },
+	{ CTL_ULONG,	KERN_PANIC_PRINT,		"panic_print" },
 	{}
 };