When entering siocnputc() with (kdb_active), don't acquire (or

release) the sio spin mutex, as use of synchronization primitives in
the debugger can result in substantial problems.  With this patch in
place entering the debugger via a serial console is made
substantially more reliable.

MFC after:	1 week
Tested by:	kris
Discussed with:	bde

1 files changed, 9 insertions, 5 deletions

diff --git a/sys/dev/sio/sio.c b/sys/dev/sio/sio.c
index ca59986..65b1029 100644
--- a/sys/dev/sio/sio.c
+++ b/sys/dev/sio/sio.c
@@ -2583,16 +2583,20 @@ siocnputc(struct consdev *cd, int c)
 	}
 	s = spltty();
 	need_unlock = 0;
-	if (sio_inited == 2 && !mtx_owned(&sio_lock)) {
-		mtx_lock_spin(&sio_lock);
-		need_unlock = 1;
+	if (!kdb_active) {
+		if (sio_inited == 2 && !mtx_owned(&sio_lock)) {
+			mtx_lock_spin(&sio_lock);
+			need_unlock = 1;
+		}
 	}
 	siocnopen(&sp, iobase, speed);
 	siocntxwait(iobase);
 	outb(iobase + com_data, c);
 	siocnclose(&sp, iobase);
-	if (need_unlock)
-		mtx_unlock_spin(&sio_lock);
+	if (!kdb_active) {
+		if (need_unlock)
+			mtx_unlock_spin(&sio_lock);
+	}
 	splx(s);
 }