Module Name: src
Committed By: ad
Date: Thu Jan 23 20:44:15 UTC 2020
Modified Files:
src/sys/kern: kern_timeout.c
Log Message:
callout_halt():
- It's a common design pattern for callouts to re-schedule themselves, so
check after waiting and put a stop to it again if needed.
- Add comments.
To generate a diff of this commit:
cvs rdiff -u -r1.57 -r1.58 src/sys/kern/kern_timeout.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_timeout.c
diff -u src/sys/kern/kern_timeout.c:1.57 src/sys/kern/kern_timeout.c:1.58
--- src/sys/kern/kern_timeout.c:1.57 Thu Nov 21 17:57:40 2019
+++ src/sys/kern/kern_timeout.c Thu Jan 23 20:44:15 2020
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_timeout.c,v 1.57 2019/11/21 17:57:40 ad Exp $ */
+/* $NetBSD: kern_timeout.c,v 1.58 2020/01/23 20:44:15 ad Exp $ */
/*-
* Copyright (c) 2003, 2006, 2007, 2008, 2009, 2019 The NetBSD Foundation, Inc.
@@ -59,7 +59,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_timeout.c,v 1.57 2019/11/21 17:57:40 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_timeout.c,v 1.58 2020/01/23 20:44:15 ad Exp $");
/*
* Timeouts are kept in a hierarchical timing wheel. The c_time is the
@@ -505,14 +505,25 @@ callout_wait(callout_impl_t *c, void *in
l = curlwp;
relock = NULL;
for (;;) {
+ /*
+ * At this point we know the callout is not pending, but it
+ * could be running on a CPU somewhere. That can be curcpu
+ * in a few cases:
+ *
+ * - curlwp is a higher priority soft interrupt
+ * - the callout blocked on a lock and is currently asleep
+ * - the callout itself has called callout_halt() (nice!)
+ */
cc = c->c_cpu;
if (__predict_true(cc->cc_active != c || cc->cc_lwp == l))
break;
+
+ /* It's running - need to wait for it to complete. */
if (interlock != NULL) {
/*
* Avoid potential scheduler lock order problems by
* dropping the interlock without the callout lock
- * held.
+ * held; then retry.
*/
mutex_spin_exit(lock);
mutex_exit(interlock);
@@ -529,7 +540,16 @@ callout_wait(callout_impl_t *c, void *in
&sleep_syncobj);
sleepq_block(0, false);
}
+
+ /*
+ * Re-lock the callout and check the state of play again.
+ * It's a common design pattern for callouts to re-schedule
+ * themselves so put a stop to it again if needed.
+ */
lock = callout_lock(c);
+ if ((c->c_flags & CALLOUT_PENDING) != 0)
+ CIRCQ_REMOVE(&c->c_list);
+ c->c_flags &= ~(CALLOUT_PENDING|CALLOUT_FIRED);
}
mutex_spin_exit(lock);
