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Message-Id: <20060805004600.2e63fcd9.akpm@osdl.org>
Date: Sat, 5 Aug 2006 00:46:00 -0700
From: Andrew Morton <akpm@...l.org>
To: Dave Jones <davej@...hat.com>
Cc: torvalds@...l.org, michal.k.k.piotrowski@...il.com,
linux-kernel@...r.kernel.org
Subject: Re: 2.6.18-rc3-g3b445eea BUG: warning at
/usr/src/linux-git/kernel/cpu.c:51/unlock_cpu_hotplug()
On Sat, 5 Aug 2006 02:47:28 -0400
Dave Jones <davej@...hat.com> wrote:
> Creating a variant of __create_workqueue that doesn't take the lock
> seems really nasty.
Honestly, the default fix for lock_cpu_hotplug() problems should be to
delete the lock_cpu_hotplug() calls and to implement local locking.
Here's a not-runtime-tested workqueue.c example.
From: Andrew Morton <akpm@...l.org>
Use a private lock instead. It protects all per-cpu data structures in
workqueue.c, including the workqueues list.
Fix a bug in schedule_on_each_cpu(): it was forgetting to lock down the
per-cpu resources.
Unfixed long-standing bug: if someone unplugs the CPU identified by
`singlethread_cpu' the kernel will get very sick.
Signed-off-by: Andrew Morton <akpm@...l.org>
---
kernel/workqueue.c | 33 +++++++++++++++++++++------------
1 file changed, 21 insertions(+), 12 deletions(-)
diff -puN kernel/workqueue.c~a kernel/workqueue.c
--- a/kernel/workqueue.c~a
+++ a/kernel/workqueue.c
@@ -68,7 +68,7 @@ struct workqueue_struct {
/* All the per-cpu workqueues on the system, for hotplug cpu to add/remove
threads to each one as cpus come/go. */
-static DEFINE_SPINLOCK(workqueue_lock);
+static DEFINE_MUTEX(workqueue_mutex);
static LIST_HEAD(workqueues);
static int singlethread_cpu;
@@ -320,10 +320,10 @@ void fastcall flush_workqueue(struct wor
} else {
int cpu;
- lock_cpu_hotplug();
+ mutex_lock(&workqueue_mutex);
for_each_online_cpu(cpu)
flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
- unlock_cpu_hotplug();
+ mutex_unlock(&workqueue_mutex);
}
}
EXPORT_SYMBOL_GPL(flush_workqueue);
@@ -371,8 +371,7 @@ struct workqueue_struct *__create_workqu
}
wq->name = name;
- /* We don't need the distraction of CPUs appearing and vanishing. */
- lock_cpu_hotplug();
+ mutex_lock(&workqueue_mutex);
if (singlethread) {
INIT_LIST_HEAD(&wq->list);
p = create_workqueue_thread(wq, singlethread_cpu);
@@ -381,9 +380,7 @@ struct workqueue_struct *__create_workqu
else
wake_up_process(p);
} else {
- spin_lock(&workqueue_lock);
list_add(&wq->list, &workqueues);
- spin_unlock(&workqueue_lock);
for_each_online_cpu(cpu) {
p = create_workqueue_thread(wq, cpu);
if (p) {
@@ -393,7 +390,7 @@ struct workqueue_struct *__create_workqu
destroy = 1;
}
}
- unlock_cpu_hotplug();
+ mutex_unlock(&workqueue_mutex);
/*
* Was there any error during startup? If yes then clean up:
@@ -434,17 +431,15 @@ void destroy_workqueue(struct workqueue_
flush_workqueue(wq);
/* We don't need the distraction of CPUs appearing and vanishing. */
- lock_cpu_hotplug();
+ mutex_lock(&workqueue_mutex);
if (is_single_threaded(wq))
cleanup_workqueue_thread(wq, singlethread_cpu);
else {
for_each_online_cpu(cpu)
cleanup_workqueue_thread(wq, cpu);
- spin_lock(&workqueue_lock);
list_del(&wq->list);
- spin_unlock(&workqueue_lock);
}
- unlock_cpu_hotplug();
+ mutex_unlock(&workqueue_mutex);
free_percpu(wq->cpu_wq);
kfree(wq);
}
@@ -515,11 +510,13 @@ int schedule_on_each_cpu(void (*func)(vo
if (!works)
return -ENOMEM;
+ mutex_lock(&workqueue_mutex);
for_each_online_cpu(cpu) {
INIT_WORK(per_cpu_ptr(works, cpu), func, info);
__queue_work(per_cpu_ptr(keventd_wq->cpu_wq, cpu),
per_cpu_ptr(works, cpu));
}
+ mutex_unlock(&workqueue_mutex);
flush_workqueue(keventd_wq);
free_percpu(works);
return 0;
@@ -635,6 +632,7 @@ static int __devinit workqueue_cpu_callb
switch (action) {
case CPU_UP_PREPARE:
+ mutex_lock(&workqueue_mutex);
/* Create a new workqueue thread for it. */
list_for_each_entry(wq, &workqueues, list) {
if (!create_workqueue_thread(wq, hotcpu)) {
@@ -653,6 +651,7 @@ static int __devinit workqueue_cpu_callb
kthread_bind(cwq->thread, hotcpu);
wake_up_process(cwq->thread);
}
+ mutex_unlock(&workqueue_mutex);
break;
case CPU_UP_CANCELED:
@@ -664,6 +663,15 @@ static int __devinit workqueue_cpu_callb
any_online_cpu(cpu_online_map));
cleanup_workqueue_thread(wq, hotcpu);
}
+ mutex_unlock(&workqueue_mutex);
+ break;
+
+ case CPU_DOWN_PREPARE:
+ mutex_lock(&workqueue_mutex);
+ break;
+
+ case CPU_DOWN_FAILED:
+ mutex_unlock(&workqueue_mutex);
break;
case CPU_DEAD:
@@ -671,6 +679,7 @@ static int __devinit workqueue_cpu_callb
cleanup_workqueue_thread(wq, hotcpu);
list_for_each_entry(wq, &workqueues, list)
take_over_work(wq, hotcpu);
+ mutex_unlock(&workqueue_mutex);
break;
}
_
-
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