exit: Add PANIC_ON_RECURSIVE_FAULT Kconfig option

If a recursive fault is detected during do_exit(), tasks are left
to sit and wait in an un-interruptible sleep until the system
reboots (typically manually). Add Kconfig option to change this
behaviour and force a panic.

This is particularly important if a critical system task encounters
a recursive fault (ex. a kworker). Otherwise, the system may be
unusable, but since the scheduler is still running system watchdogs
may continue to be pet.

Change-Id: Ifc26fc79d6066f05a3b2c4d27f78bf4f8d2bd640
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>

kernel/exit.c

@@ -797,7 +797,11 @@ void __noreturn do_exit(long code)
 	 * leave this task alone and wait for reboot.
 	 */
 	if (unlikely(tsk->flags & PF_EXITING)) {
+#ifdef CONFIG_PANIC_ON_RECURSIVE_FAULT
+		panic("Recursive fault!\n");
+#else
 		pr_alert("Fixing recursive fault but reboot is needed!\n");
+#endif
 		/*
 		 * We can do this unlocked here. The futex code uses
 		 * this flag just to verify whether the pi state

lib/Kconfig.debug

@@ -879,6 +879,17 @@ config BOOTPARAM_SOFTLOCKUP_PANIC_VALUE
 	default 0 if !BOOTPARAM_SOFTLOCKUP_PANIC
 	default 1 if BOOTPARAM_SOFTLOCKUP_PANIC
 
+config PANIC_ON_RECURSIVE_FAULT
+	bool "Panic on recursive faults during task exit"
+	help
+	  Panic upon the detection of a recursive fault during task exit,
+	  rather than putting the task into an uninterruptible sleep.
+	  This is particularly useful for debugging system hangs in
+	  scenarios where the task experiencing the fault is critical
+	  for system operation, rendering the system inoperable.
+
+	  Say N if unsure.
+
 config DETECT_HUNG_TASK
 	bool "Detect Hung Tasks"
 	depends on DEBUG_KERNEL