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On Dec 21, 2007, at 10:27, Chris Ross wrote:
> On Dec 21, 2007, at 07:54, Matt Fleming wrote:
>> On Fri, Dec 21, 2007 at 12:36:49PM +0000, Robert Swindells wrote:
>>>> bt
>>> lockdebug_abort(...)
>>> mutex_vector_enter(...)
>>> zstty_softint(...) at zstty_softint+0x10
>>
>> The tty_lock mutex was already entered in zsopen() and  
>> zstty_softint()
>> tries to enter it again.
>>
>> Is it just safe to remove the calls to mutex_spin_{enter/exit} in
>> zstty_softint(), since tty_lock is held throughout anyway and I can't
>> see any other code that calls zstty_softint?
>
>   Whether or not that is safe, it doesn't solve the problem in its
> entirety.
> db> bt
> lockdebug_abort(...) at netbsd:lockdebug_abort+0x54
> mutex_vector_enter(...) at netbsd:mutex_vector_enter+0x158
> nullmodem(...) at netbsd:nullmodem+0x8
> zstty_softint(...) at netbsd:zstty_softint+0x380
> zsparam(...) at netbsd:zsparam+0x218
> zsopen(...) at netbsd:zsopen+0x200

   So, I looked into this a little more.  There are mutex_spin_enter()
and mutex_spin_exit() calls in sys/kern/tty.c in both nullmodem() and
ttymodem().  Either or both of those will cause the same:

Mutex error: mutex_vector_enter: locking against myself

   crash if the calls are only removed from zstty_softint().  I
experimented with taking those out as well, despite presuming that
was the "wrong thing to do," and the machine comes up to multi-user,
but crashes with an unlocked mutex as soon as I try to log in.

   The following change to sys/dev/ic/z8530tty.c causes the machine
to come up multi-user, and I can ssh in and do things.  But, I was
just guessing at something to try, and would want someone who knows
much more about the recent vmlocking branch merges to give an
opinion.  Andrew?

                          - Chris



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Index: sys/dev/ic/z8530tty.c
===================================================================
RCS file: /cvsroot/src/sys/dev/ic/z8530tty.c,v
retrieving revision 1.117
diff -u -r1.117 z8530tty.c
--- sys/dev/ic/z8530tty.c	19 Nov 2007 18:51:48 -0000	1.117
+++ sys/dev/ic/z8530tty.c	22 Dec 2007 05:38:58 -0000
@@ -1886,7 +1886,9 @@
 		/*
 		 * Inform the tty layer that carrier detect changed.
 		 */
+		mutex_spin_exit(&tty_lock);
 		(void) (*tp->t_linesw->l_modem)(tp, ISSET(rr0, ZSRR0_DCD));
+		mutex_spin_enter(&tty_lock);
 	}
 
 	if (ISSET(delta, cs->cs_rr0_cts)) {
@@ -1919,8 +1921,6 @@
 	struct zstty_softc *zst = cs->cs_private;
 	struct tty *tp = zst->zst_tty;
 
-	mutex_spin_enter(&tty_lock);
-
 	if (zst->zst_rx_ready) {
 		zst->zst_rx_ready = 0;
 		zstty_rxsoft(zst, tp);
@@ -1935,8 +1935,6 @@
 		zst->zst_tx_done = 0;
 		zstty_txsoft(zst, tp);
 	}
-
-	mutex_spin_exit(&tty_lock);
 }
 
 struct zsops zsops_tty = {

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