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Subject[PATCH 3/5] lock_cpu_hotplug:Redesign - Use lock_cpu_hotplug in workqueue.c instead of workqueue_mutex.
Use lock_cpu_hotplug() instead of workqueue_mutex to prevent a 
cpu-hotplug event in kernel/workqueue.c.

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>

---
kernel/workqueue.c | 37 +++++++++++++------------------------
1 files changed, 13 insertions(+), 24 deletions(-)

Index: hotplug/kernel/workqueue.c
===================================================================
--- hotplug.orig/kernel/workqueue.c
+++ hotplug/kernel/workqueue.c
@@ -67,9 +67,7 @@ struct workqueue_struct {
struct list_head list; /* Empty if single thread */
};

-/* All the per-cpu workqueues on the system, for hotplug cpu to add/remove
- threads to each one as cpus come/go. */
-static DEFINE_MUTEX(workqueue_mutex);
+static DEFINE_SPINLOCK(workqueue_lock);
static LIST_HEAD(workqueues);

static int singlethread_cpu;
@@ -328,10 +326,10 @@ void fastcall flush_workqueue(struct wor
} else {
int cpu;

- mutex_lock(&workqueue_mutex);
+ lock_cpu_hotplug();
for_each_online_cpu(cpu)
flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
- mutex_unlock(&workqueue_mutex);
+ unlock_cpu_hotplug();
}
}
EXPORT_SYMBOL_GPL(flush_workqueue);
@@ -379,7 +377,7 @@ struct workqueue_struct *__create_workqu
}

wq->name = name;
- mutex_lock(&workqueue_mutex);
+ lock_cpu_hotplug();
if (singlethread) {
INIT_LIST_HEAD(&wq->list);
p = create_workqueue_thread(wq, singlethread_cpu);
@@ -388,7 +386,9 @@ 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) {
@@ -398,8 +398,7 @@ struct workqueue_struct *__create_workqu
destroy = 1;
}
}
- mutex_unlock(&workqueue_mutex);
-
+ unlock_cpu_hotplug();
/*
* Was there any error during startup? If yes then clean up:
*/
@@ -439,15 +438,17 @@ void destroy_workqueue(struct workqueue_
flush_workqueue(wq);

/* We don't need the distraction of CPUs appearing and vanishing. */
- mutex_lock(&workqueue_mutex);
+ lock_cpu_hotplug();
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);
}
- mutex_unlock(&workqueue_mutex);
+ unlock_cpu_hotplug();
free_percpu(wq->cpu_wq);
kfree(wq);
}
@@ -519,13 +520,13 @@ int schedule_on_each_cpu(void (*func)(vo
if (!works)
return -ENOMEM;

- mutex_lock(&workqueue_mutex);
+ lock_cpu_hotplug();
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);
+ unlock_cpu_hotplug();
flush_workqueue(keventd_wq);
free_percpu(works);
return 0;
@@ -641,7 +642,6 @@ 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)) {
@@ -660,7 +660,6 @@ 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:
@@ -672,15 +671,6 @@ 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:
@@ -688,7 +678,6 @@ 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;
}

--
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
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