Module Name: src
Committed By: yamt
Date: Fri Jun 15 13:51:41 UTC 2012
Modified Files:
src/sys/kern: kern_turnstile.c
Log Message:
comments and assertions.
no functional changes.
To generate a diff of this commit:
cvs rdiff -u -r1.31 -r1.32 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:1.31 src/sys/kern/kern_turnstile.c:1.32
--- src/sys/kern/kern_turnstile.c:1.31 Fri Dec 2 12:31:53 2011
+++ src/sys/kern/kern_turnstile.c Fri Jun 15 13:51:40 2012
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_turnstile.c,v 1.31 2011/12/02 12:31:53 yamt Exp $ */
+/* $NetBSD: kern_turnstile.c,v 1.32 2012/06/15 13:51:40 yamt 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 1.31 2011/12/02 12:31:53 yamt Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_turnstile.c,v 1.32 2012/06/15 13:51:40 yamt Exp $");
#include <sys/param.h>
#include <sys/lockdebug.h>
@@ -199,7 +199,9 @@ turnstile_exit(wchan_t obj)
*
* Lend our priority to lwps on the blocking chain.
*
- *
+ * If the current owner of the lock (l->l_wchan, set by sleepq_enqueue)
+ * has a priority lower than ours (lwp_eprio(l)), lend our priority to
+ * him to avoid priority inversions.
*/
static void
@@ -225,29 +227,37 @@ turnstile_lendpri(lwp_t *cur)
if (l->l_wchan == NULL)
break;
+ /*
+ * Ask syncobj the owner of the lock.
+ */
owner = (*l->l_syncobj->sobj_owner)(l->l_wchan);
if (owner == NULL)
break;
- /* The owner may have changed as we have dropped the tc lock */
+ /*
+ * 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
+ * We own the lock: stop here, sleepq_block()
+ * should wake up immediatly.
*/
break;
}
- if (l->l_mutex != owner->l_mutex)
- dolock = true;
- else
- dolock = false;
+ /*
+ * Acquire owner->l_mutex if we don't have it yet.
+ * Because we already have another LWP lock (l->l_mutex) held,
+ * we need to play a try lock dance to avoid deadlock.
+ */
+ dolock = l->l_mutex != owner->l_mutex;
if (l == owner || (dolock && !lwp_trylock(owner))) {
/*
- * restart from curlwp.
+ * The owner was changed behind us or trylock failed.
+ * 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.
+ * 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;
@@ -255,11 +265,20 @@ turnstile_lendpri(lwp_t *cur)
prio = lwp_eprio(l);
continue;
}
+ /*
+ * If the owner's priority is already higher than ours,
+ * there's nothing to do anymore.
+ */
if (prio <= lwp_eprio(owner)) {
if (dolock)
lwp_unlock(owner);
break;
}
+ /*
+ * Lend our priority to the 'owner' LWP.
+ *
+ * Update lenders info for turnstile_unlendpri.
+ */
ts = l->l_ts;
KASSERT(ts->ts_inheritor == owner || ts->ts_inheritor == NULL);
if (ts->ts_inheritor == NULL) {
@@ -273,6 +292,7 @@ turnstile_lendpri(lwp_t *cur)
}
if (dolock)
lwp_unlock(l);
+ LOCKDEBUG_BARRIER(owner->l_mutex, 1);
l = owner;
}
LOCKDEBUG_BARRIER(l->l_mutex, 1);
