Add a new kernel option RESTARTABLE_PANICS. If this option is present,

then one can restart from a panic by resetting the panicstr variable to
NULL.  This commit conditionalizes the previously committed functionality
on this variable.  It also removes the __dead2 attribute from the panic()
function so that when one continues from a panic() the behavior will
be predictable.

sys/conf/NOTES

@@ -387,6 +387,16 @@ options 	DIAGNOSTIC
 #
 options		REGRESSION
 
+#
+# RESTARTABLE_PANICS allows one to continue from a panic as if it were
+# a call to the debugger via the Debugger() function instead.  It is only
+# useful if a kernel debugger is present.  To restart from a panic, reset
+# the panicstr variable to NULL and continue execution.  This option is
+# for development use only and should NOT be used in production systems
+# to "workaround" a panic.
+#
+options 	RESTARTABLE_PANICS
+
 #
 # PERFMON causes the driver for Pentium/Pentium Pro performance counters
 # to be compiled.  See perfmon(4) for more information.

sys/conf/options

@@ -387,6 +387,7 @@ ENABLE_VFS_IOOPT	opt_global.h
 INVARIANT_SUPPORT	opt_global.h
 INVARIANTS		opt_global.h
 REGRESSION		opt_global.h
+RESTARTABLE_PANICS	opt_global.h
 SIMPLELOCK_DEBUG	opt_global.h
 VFS_BIO_DEBUG		opt_global.h
 

sys/i386/conf/NOTES

@@ -387,6 +387,16 @@ options 	DIAGNOSTIC
 #
 options		REGRESSION
 
+#
+# RESTARTABLE_PANICS allows one to continue from a panic as if it were
+# a call to the debugger via the Debugger() function instead.  It is only
+# useful if a kernel debugger is present.  To restart from a panic, reset
+# the panicstr variable to NULL and continue execution.  This option is
+# for development use only and should NOT be used in production systems
+# to "workaround" a panic.
+#
+options 	RESTARTABLE_PANICS
+
 #
 # PERFMON causes the driver for Pentium/Pentium Pro performance counters
 # to be compiled.  See perfmon(4) for more information.

sys/kern/kern_shutdown.c

@@ -610,6 +610,7 @@ panic(const char *fmt, ...)
 #if defined(DDB)
 	if (debugger_on_panic)
 		Debugger ("panic");
+#ifdef RESTARTABLE_PANICS
 	/* See if the user aborted the panic, in which case we continue. */
 	if (panicstr == NULL) {
 #ifdef SMP
@@ -617,6 +618,7 @@ panic(const char *fmt, ...)
 #endif
 		return;
 	}
+#endif
 #endif
 	boot(bootopt);
 }

sys/sys/param.h

@@ -236,6 +236,10 @@
  * things that included sys/systm.h just for panic().
  */
 #ifdef _KERNEL
+#ifdef RESTARTABLE_PANICS
+void	panic __P((const char *, ...)) __printflike(1, 2);
+#else
 void	panic __P((const char *, ...)) __dead2 __printflike(1, 2);
 #endif
+#endif
 #endif	/* _SYS_PARAM_H_ */