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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.
This commit is contained in:
ad 2020-01-23 20:44:15 +00:00
parent e9c617f5ed
commit 5f882f3427
1 changed files with 23 additions and 3 deletions
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26
sys/kern/kern_timeout.c
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@ -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 *interlock, kmutex_t *lock)
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 *interlock, kmutex_t *lock)
&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);