The "cnputs_mtx" mutex must be allowed to recurse. Debug prints and/or

witness printouts in the console driver clients can cause this mutex
to recurse by calls to "printf()" from witness for example. In
particular this can happen if "debug.witness.skipspin=0" is set in the
boot environment.

MFC after:	1 week

1 files changed, 7 insertions, 1 deletions

diff --git a/sys/kern/kern_cons.c b/sys/kern/kern_cons.c
index bbc0e51..75f9c18 100644
--- a/sys/kern/kern_cons.c
+++ b/sys/kern/kern_cons.c
@@ -601,7 +601,13 @@ static void
 cn_drvinit(void *unused)
 {
 
-	mtx_init(&cnputs_mtx, "cnputs_mtx", NULL, MTX_SPIN | MTX_NOWITNESS);
+	/*
+	 * NOTE: Debug prints and/or witness printouts in console
+	 * driver clients can cause the "cnputs_mtx" mutex to
+	 * recurse. Make sure the "MTX_RECURSE" flags is set!
+	 */
+	mtx_init(&cnputs_mtx, "cnputs_mtx", NULL, MTX_SPIN |
+	    MTX_NOWITNESS | MTX_RECURSE);
 	use_cnputs_mtx = 1;
 }