svn commit: r367848 - in head: share/man/man4 sys/kern

[Mitchell Horne]

Author: mhorne
Date: Thu Nov 19 18:03:40 2020
New Revision: 367848
URL: https://svnweb.freebsd.org/changeset/base/367848

Log:
  Add an option for entering KDB on recursive panics
  
  There are many cases where one would choose avoid entering the debugger
  on a normal panic, opting instead to reboot and possibly save a kernel
  dump. However, recursive kernel panics are an unusual case that might
  warrant attention from a human, so provide a secondary tunable,
  debug.debugger_on_recursive_panic, to allow entering the debugger only
  when this occurs.
  
  For for simplicity in maintaining existing behaviour, the tunable
  defaults to zero.
  
  Reviewed by:	cem, markj
  Sponsored by:	NetApp, Inc.
  Sponsored by:	Klara, Inc.
  Differential Revision:	https://reviews.freebsd.org/D27271

Modified:
  head/share/man/man4/ddb.4
  head/sys/kern/kern_shutdown.c

Modified: head/share/man/man4/ddb.4
==============================================================================
--- head/share/man/man4/ddb.4	Thu Nov 19 17:54:41 2020	(r367847)
+++ head/share/man/man4/ddb.4	Thu Nov 19 18:03:40 2020	(r367848)
@@ -26,7 +26,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd October 17, 2019
+.Dd November 19, 2020
 .Dt DDB 4
 .Os
 .Sh NAME
@@ -87,6 +87,16 @@ which is the default
 unless the
 .Dv KDB_UNATTENDED
 option is specified.
+Similarly, if the
+.Va debug.debugger_on_recursive_panic
+variable is set to
+.Dv 1 ,
+then the debugger will be invoked on a recursive kernel panic.
+This variable has a default value of
+.Dv 0 ,
+and has no effect if
+.Va debug.debugger_on_panic
+is already set non-zero.
 .Pp
 The current location is called
 .Va dot .

Modified: head/sys/kern/kern_shutdown.c
==============================================================================
--- head/sys/kern/kern_shutdown.c	Thu Nov 19 17:54:41 2020	(r367847)
+++ head/sys/kern/kern_shutdown.c	Thu Nov 19 18:03:40 2020	(r367848)
@@ -127,6 +127,11 @@ SYSCTL_INT(_debug, OID_AUTO, debugger_on_panic,
     CTLFLAG_RWTUN | CTLFLAG_SECURE,
     &debugger_on_panic, 0, "Run debugger on kernel panic");
 
+static bool debugger_on_recursive_panic = false;
+SYSCTL_BOOL(_debug, OID_AUTO, debugger_on_recursive_panic,
+    CTLFLAG_RWTUN | CTLFLAG_SECURE,
+    &debugger_on_recursive_panic, 0, "Run debugger on recursive kernel panic");
+
 int debugger_on_trap = 0;
 SYSCTL_INT(_debug, OID_AUTO, debugger_on_trap,
     CTLFLAG_RWTUN | CTLFLAG_SECURE,
@@ -899,6 +904,8 @@ vpanic(const char *fmt, va_list ap)
 		kdb_backtrace();
 	if (debugger_on_panic)
 		kdb_enter(KDB_WHY_PANIC, "panic");
+	else if (!newpanic && debugger_on_recursive_panic)
+		kdb_enter(KDB_WHY_PANIC, "re-panic");
 #endif
 	/*thread_lock(td); */
 	td->td_flags |= TDF_INPANIC;