Module Name: src
Committed By: bouyer
Date: Sun Sep 13 14:38:20 UTC 2009
Modified Files:
src/sys/kern: kern_turnstile.c
Log Message:
PR kern/41923: assertion "cur != owner" failed
In the for(;;) loop of turnstile_block(), the lock owner can change while
cur's lock is released (cur's lock is also the tschain_t's mutex).
Remove the KASSERT about owner being invariant and try to deal with the
fact that the owner can change instead.
http://mail-index.netbsd.org/tech-kern/2009/08/24/msg005957.html
and followups.
To generate a diff of this commit:
cvs rdiff -u -r1.24 -r1.25 src/sys/kern/kern_turnstile.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/kern_turnstile.c
diff -u src/sys/kern/kern_turnstile.c:1.24 src/sys/kern/kern_turnstile.c:1.25
--- src/sys/kern/kern_turnstile.c:1.24 Sat Mar 21 13:11:14 2009
+++ src/sys/kern/kern_turnstile.c Sun Sep 13 14:38:20 2009
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_turnstile.c,v 1.24 2009/03/21 13:11:14 ad Exp $ */
+/* $NetBSD: kern_turnstile.c,v 1.25 2009/09/13 14:38:20 bouyer Exp $ */
/*-
* Copyright (c) 2002, 2006, 2007, 2009 The NetBSD Foundation, Inc.
@@ -60,7 +60,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_turnstile.c,v 1.24 2009/03/21 13:11:14 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_turnstile.c,v 1.25 2009/09/13 14:38:20 bouyer Exp $");
#include <sys/param.h>
#include <sys/lockdebug.h>
@@ -253,6 +253,7 @@
sq = &ts->ts_sleepq[q];
ts->ts_waiters[q]++;
sleepq_enter(sq, l, tc->tc_mutex);
+ /* now tc->tc_mutex is also cur->l_mutex and l->l_mutex */
LOCKDEBUG_BARRIER(tc->tc_mutex, 1);
l->l_kpriority = true;
obase = l->l_kpribase;
@@ -275,6 +276,7 @@
* compiling a kernel with LOCKDEBUG to pinpoint the problem.
*/
prio = lwp_eprio(l);
+
for (;;) {
bool dolock;
@@ -285,9 +287,24 @@
if (owner == NULL)
break;
- KASSERT(l != owner);
- KASSERT(cur != owner);
+ /* The owner may have changed as we have dropped the tc lock */
+ if (cur == owner) {
+ /*
+ * we own the lock: stop here, sleepq_block()
+ * should wake up immediatly
+ */
+ break;
+ }
+ if (l == owner) {
+ /* owner has changed, restart from curlwp */
+ lwp_unlock(l);
+ l = cur;
+ lwp_lock(l);
+ prio = lwp_eprio(l);
+ continue;
+ }
+
if (l->l_mutex != owner->l_mutex)
dolock = true;
else
@@ -295,6 +312,10 @@
if (dolock && !lwp_trylock(owner)) {
/*
* restart from curlwp.
+ * Note that there may be a livelock here:
+ * the owner may try grabing cur's lock (which is
+ * the tc lock) while we're trying to grab
+ * the owner's lock.
*/
lwp_unlock(l);
l = cur;
