svn commit: r332860 - head/sys/kern

[Jonathan T. Looney]

Author: jtl
Date: Sat Apr 21 17:05:00 2018
New Revision: 332860
URL: https://svnweb.freebsd.org/changeset/base/332860

Log:
  When running with INVARIANTS, the kernel contains extra checks.  However,
  these assumptions may not hold true once we've panic'd. Therefore, the
  checks hold less value after a panic.  Additionally, if one of the checks
  fails while we are already panic'd, this creates a double-panic which can
  interfere with debugging the original panic.
  
  Therefore, this commit allows an administrator to suppress a response to
  KASSERT checks after a panic by setting a tunable/sysctl.  The
  tunable/sysctl (debug.kassert.suppress_in_panic) defaults to being
  enabled.
  
  Reviewed by:	kib
  Sponsored by:	Netflix, Inc.
  Differential Revision:	https://reviews.freebsd.org/D12920

Modified:
  head/sys/kern/kern_shutdown.c

Modified: head/sys/kern/kern_shutdown.c
==============================================================================
--- head/sys/kern/kern_shutdown.c	Sat Apr 21 15:15:47 2018	(r332859)
+++ head/sys/kern/kern_shutdown.c	Sat Apr 21 17:05:00 2018	(r332860)
@@ -642,6 +642,7 @@ static int kassert_do_log = 1;
 static int kassert_log_pps_limit = 4;
 static int kassert_log_mute_at = 0;
 static int kassert_log_panic_at = 0;
+static int kassert_suppress_in_panic = 1;
 static int kassert_warnings = 0;
 
 SYSCTL_NODE(_debug, OID_AUTO, kassert, CTLFLAG_RW, NULL, "kassert options");
@@ -676,6 +677,10 @@ SYSCTL_INT(_debug_kassert, OID_AUTO, log_pps_limit, CT
 SYSCTL_INT(_debug_kassert, OID_AUTO, log_mute_at, CTLFLAG_RWTUN,
     &kassert_log_mute_at, 0, "max number of KASSERTS to log");
 
+SYSCTL_INT(_debug_kassert, OID_AUTO, suppress_in_panic, CTLFLAG_RWTUN,
+    &kassert_suppress_in_panic, 0,
+    "KASSERTs will be suppressed while handling a panic");
+
 static int kassert_sysctl_kassert(SYSCTL_HANDLER_ARGS);
 
 SYSCTL_PROC(_debug_kassert, OID_AUTO, kassert,
@@ -707,6 +712,10 @@ kassert_panic(const char *fmt, ...)
 {
 	static char buf[256];
 	va_list ap;
+
+	/* If we already panic'd, don't create a double-fault. */
+	if (panicstr != NULL && kassert_suppress_in_panic)
+		return;
 
 	va_start(ap, fmt);
 	(void)vsnprintf(buf, sizeof(buf), fmt, ap);