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/[email protected]
Signed-off-by: Feng Tang <[email protected]>
Suggested-by: Steven Rostedt <[email protected]>
Acked-by: Steven Rostedt (VMware) <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: John Stultz <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Kees Cook <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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