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>

Documentation/sysctl/kernel.txt

@@ -60,6 +60,7 @@ show up in /proc/sys/kernel:
 - panic_on_stackoverflow
 - panic_on_unrecovered_nmi
 - panic_on_warn
+- panic_print
 - panic_on_rcu_stall
 - perf_cpu_time_max_percent
 - perf_event_paranoid
@@ -654,6 +655,22 @@ a kernel rebuild when attempting to kdump at the location of a WARN().
 
 ==============================================================
 
+panic_print:
+
+Bitmask for printing system info when panic happens. User can chose
+combination of the following bits:
+
+bit 0: print all tasks info
+bit 1: print system memory info
+bit 2: print timer info
+bit 3: print locks info if CONFIG_LOCKDEP is on
+bit 4: print ftrace buffer
+
+So for example to print tasks and memory info on panic, user can:
+  echo 3 > /proc/sys/kernel/panic_print
+
+==============================================================
+
 panic_on_rcu_stall:
 
 When set to 1, calls panic() after RCU stall detection messages. This

include/linux/kernel.h

@@ -527,6 +527,7 @@ static inline u32 int_sqrt64(u64 x)
 extern void bust_spinlocks(int yes);
 extern int oops_in_progress;		/* If set, an oops, panic(), BUG() or die() is in progress */
 extern int panic_timeout;
+extern unsigned long panic_print;
 extern int panic_on_oops;
 extern int panic_on_unrecovered_nmi;
 extern int panic_on_io_nmi;

include/uapi/linux/sysctl.h

@@ -153,6 +153,7 @@ enum
 	KERN_NMI_WATCHDOG=75, /* int: enable/disable nmi watchdog */
 	KERN_PANIC_ON_NMI=76, /* int: whether we will panic on an unrecovered */
 	KERN_PANIC_ON_WARN=77, /* int: call panic() in WARN() functions */
+	KERN_PANIC_PRINT=78, /* ulong: bitmask to print system info on panic */
 };
 
 

kernel/panic.c

@@ -51,7 +51,7 @@ EXPORT_SYMBOL_GPL(panic_timeout);
 #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);
 

kernel/sysctl.c

@@ -807,6 +807,13 @@ static struct ctl_table kern_table[] = {
 		.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",

kernel/sysctl_binary.c

@@ -140,6 +140,7 @@ static const struct bin_table bin_kern_table[] = {
 	{ 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" },
 	{}
 };