项目需要,在驱动模块里用内核计时器timer_list实现了一个状态机。
郁闷的是,运行时总报错“Scheduling while atomic”,网上搜了一下:
"Scheduling while atomic" indicates that you've tried to sleep somewhere that you shouldn't - like within a spinlock-protected critical section or an interrupt handler.
改进程序,在计时器里使用了workqueue,搞定问题。顺便把workqueue的实现代码总结了一下
一、workqueue简介workqueue与tasklet类似,都是允许内核代码请求某个函数在将来的时间被调用(抄《ldd3》上的)
每个workqueue就是一个内核进程。workqueue与tasklet的区别:
1.tasklet是通过软中断实现的,在软中断上下文中运行,tasklet代码必须是原子的
workqueue是通过内核进程实现的,就没有上述限制的,最爽的是,工作队列函数可以休眠
PS: 我的驱动模块就是印在计时器中调用了可休眠函数,所以出现了cheduling while atomic告警
内核计时器也是通过软中断实现的
2.tasklet始终运行在被初始提交的同一处理器上,workqueue不一定
3.tasklet不能确定延时时间(即使很短),workqueue可以设定延迟时间
二、workqueue的API workqueue的API自2.6.20后发生了变化
- #include <linux/workqueue.h>
-
struct workqueue_struct;
-
struct work_struct;
-
-
struct workqueue_struct *create_workqueue(const char *name);
-
void destroy_workqueue(struct workqueue_struct *queue);
-
-
INIT_WORK(_work, _func);
-
INIT_DELAYED_WORK(_work, _func);
-
-
int queue_work(struct workqueue_struct *wq, struct work_struct *work);
-
int queue_delayed_work(struct workqueue_struct *wq,struct delayed_work *dwork, unsigned long delay);
-
-
int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
-
struct delayed_work *dwork, unsigned long delay);
-
-
int cancel_work_sync(struct work_struct *work);
-
int cancel_delayed_work_sync(struct delayed_work *dwork);
-
-
void flush_workqueue(struct workqueue_struct *wq);
Workqueue编程接口
序号
|
接口函数
|
说明
|
1
|
create_workqueue
|
用于创建一个workqueue队列,为系统中的每个CPU都创建一个内核线程。输入参数:
@name:workqueue的名称
|
2
|
create_singlethread_workqueue
|
用于创建workqueue,只创建一个内核线程。输入参数:
@name:workqueue名称
|
3
|
destroy_workqueue
|
释放workqueue队列。输入参数:
@ workqueue_struct:需要释放的workqueue队列指针
|
4
|
schedule_work
|
调度执行一个具体的任务,执行的任务将会被挂入Linux系统提供的workqueue——keventd_wq输入参数:
@ work_struct:具体任务对象指针
|
5
|
schedule_delayed_work
|
延迟一定时间去执行一个具体的任务,功能与schedule_work类似,多了一个延迟时间,输入参数:
@work_struct:具体任务对象指针
@delay:延迟时间
|
6
|
queue_work
|
调度执行一个指定workqueue中的任务。输入参数:
@ workqueue_struct:指定的workqueue指针
@work_struct:具体任务对象指针
|
7
|
queue_delayed_work
|
延迟调度执行一个指定workqueue中的任务,功能与queue_work类似,输入参数多了一个delay。 |
下面实例是不指定delay时间的workqueue
(代码基于2.6.24)
- struct my_work_stuct{
-
int test;
-
struct work_stuct save;
-
};
-
-
struct my_work_stuct test_work;
-
struct workqueue_struct *test_workqueue;
-
-
void do_save(struct work_struct *p_work)
-
{
-
struct my_work_struct *p_test_work = container_of(p_work, struct my_work_stuct, save);
-
printk("%d\n",p_test_work->test);
-
}
-
-
void test_init()
-
{
-
test_workqueue = create_workqueue("test_workqueue");
-
if (!test_workqueue)
-
panic("Failed to create test_workqueue\n");
-
-
INIT_WORK(&(test_work.save), do_save);
-
-
queue_work(test_workqueue, &(test_work.save));
-
}
-
-
void test_destory(void)
-
{
-
if(test_workqueue)
-
destroy_workqueue(test_workqueue);
-
}
三、workqueue的实现工作队列workqueue不是通过软中断实现的,它是通过内核进程实现的
首先,创建一个workqueue,实际上就是建立一个内核进程
- create_workqueue("tap_workqueue")
-
--> __create_workqueue(“tap_workqueue”, 0, 0)
-
--> __create_workqueue_key((name), (singlethread), (freezeable), NULL, NULL){
-
wq = kzalloc(sizeof(*wq), GFP_KERNEL);
-
wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
-
wq->name = name;
-
wq->singlethread = singlethread;
-
wq->freezeable = freezeable;
-
INIT_LIST_HEAD(&wq->list);
-
-
for_each_possible_cpu(cpu) {
-
cwq = init_cpu_workqueue(wq, cpu);
-
err = create_workqueue_thread(cwq, cpu);
-
start_workqueue_thread(cwq, cpu);
-
}
-
}
create_workqueue_thread 建立了一个内核进程 worker_thread(linux_2_6_24/kernel/workqueue.c)
- create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
-
{
-
struct workqueue_struct *wq = cwq->wq;
-
-
const char *fmt = is_single_threaded(wq) ? "%s" : "%s/%d";
-
struct task_struct *p;
-
-
p = kthread_create(worker_thread, cwq, fmt, wq->name, cpu);
-
-
if (IS_ERR(p))
-
return PTR_ERR(p);
-
-
cwq->thread = p;
-
-
return 0;
-
}
内核进程worker_thread做的事情很简单,死循环而已,不停的执行workqueue上的work_list
(linux_2_6_24/kernel/workqueue.c)
- int worker_thread (void *__cwq)
-
{
-
struct cpu_workqueue_struct *cwq = __cwq;
-
/*下面定义等待队列项*/
-
DEFINE_WAIT(wait);
-
-
/*下面freezeable一般为0*/
-
if (cwq->wq->freezeable)
-
set_freezable();
-
-
/*提高优先级别*/
-
set_user_nice(current, -5);
-
-
for (;;) {
-
/*在cwq->more_work上等待, 若有人调用queue_work,该函数将调用wake_up(&cwq->more_work) 激活本进程*/
-
prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE);
-
-
/*work队列空则切换出去*/
-
if (!freezing(current) && !kthread_should_stop() && list_empty(&cwq->worklist))
-
schedule();
-
-
-
/*切换回来则结束等待 说明有人唤醒cwq->more_work上的等待 有work需要处理*/
-
finish_wait(&cwq->more_work, &wait);
-
-
/*下面空,因为没有定义电源管理*/
-
try_to_freeze();
-
-
if (kthread_should_stop())
-
break;
-
-
/*run_workqueue依次处理工作队列上所有的work*/
-
run_workqueue(cwq);
-
}
-
return 0;
-
}
-
-
-
/*run_workqueue依次处理工作队列上所有的work*/
-
static void run_workqueue(struct cpu_workqueue_struct *cwq)
-
{
-
spin_lock_irq(&cwq->lock);
-
cwq->run_depth++;
-
if (cwq->run_depth > 3) {
-
/* morton gets to eat his hat */
-
printk("%s: recursion depth exceeded: %d\n",
-
__FUNCTION__, cwq->run_depth);
-
dump_stack();
-
}
-
-
while (!list_empty(&cwq->worklist)) {
-
struct work_struct *work = list_entry(cwq->worklist.next,
-
struct work_struct, entry);
-
work_func_t f = work->func;
-
#ifdef CONFIG_LOCKDEP
-
/*
-
* It is permissible to free the struct work_struct
-
* from inside the function that is called from it,
-
* this we need to take into account for lockdep too.
-
* To avoid bogus "held lock freed" warnings as well
-
* as problems when looking into work->lockdep_map,
-
* make a copy and use that here.
-
*/
-
struct lockdep_map lockdep_map = work->lockdep_map;
-
#endif
-
-
cwq->current_work = work;
-
list_del_init(cwq->worklist.next);
-
spin_unlock_irq(&cwq->lock);
-
-
BUG_ON(get_wq_data(work) != cwq);
-
work_clear_pending(work);
-
lock_acquire(&cwq->wq->lockdep_map, 0, 0, 0, 2, _THIS_IP_);
-
lock_acquire(&lockdep_map, 0, 0, 0, 2, _THIS_IP_);
-
-
f(work); /*执行work项中的func*/
-
-
lock_release(&lockdep_map, 1, _THIS_IP_);
-
lock_release(&cwq->wq->lockdep_map, 1, _THIS_IP_);
-
-
if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
-
printk(KERN_ERR "BUG: workqueue leaked lock or atomic: "
-
"%s/0x%08x/%d\n",
-
current->comm, preempt_count(),
-
task_pid_nr(current));
-
printk(KERN_ERR " last function: ");
-
print_symbol("%s\n", (unsigned long)f);
-
debug_show_held_locks(current);
-
dump_stack();
-
}
-
-
spin_lock_irq(&cwq->lock);
-
cwq->current_work = NULL;
-
}
-
cwq->run_depth--;
-
spin_unlock_irq(&cwq->lock);
-
}
将一个work加入到指定workqueue的work_list中(文件linux_2_6_24
/kernel
/workqueue
.c)
int fastcall queue_work(struct workqueue_struct *wq, struct work_struct *work)
-
{
-
int ret = 0;
-
-
if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
-
BUG_ON(!list_empty(&work->entry));
-
__queue_work(wq_per_cpu(wq, get_cpu()), work);
-
put_cpu();
-
ret = 1;
-
}
-
return ret;
-
}
-
-
-
/* Preempt must be disabled. */
-
static void __queue_work(struct cpu_workqueue_struct *cwq, struct work_struct *work)
-
{
-
unsigned long flags;
-
-
spin_lock_irqsave(&cwq->lock, flags);
-
insert_work(cwq, work, 1);
-
spin_unlock_irqrestore(&cwq->lock, flags);
-
}
-
-
static void insert_work(struct cpu_workqueue_struct *cwq,
-
struct work_struct *work, int tail)
-
{
-
set_wq_data(work, cwq);
-
/*
-
* Ensure that we get the right work->data if we see the
-
* result of list_add() below, see try_to_grab_pending().
-
*/
-
smp_wmb();
-
if (tail)
-
list_add_tail(&work->entry, &cwq->worklist);
-
else
-
list_add(&work->entry, &cwq->worklist);
-
wake_up(&cwq->more_work);
-
}
四、共享队列其实内核有自己的一个workqueue,叫keventd_wq,这个工作队列也叫做“共享队列”。
do_basic_setup --> init_workqueues --> create_workqueue("events");
若驱动模块使用的workqueue功能很简单的话,可以使用“共享队列”,不用自己再建一个队列
使用共享队列,有这样一套API
- int schedule_work(struct work_struct *work)
-
{
-
queue_work(keventd_wq, work);
-
}
-
-
int schedule_delayed_work(struct delayed_work *dwork,unsigned long delay)
-
{
-
timer_stats_timer_set_start_info(&dwork->timer);
-
return queue_delayed_work(keventd_wq, dwork, delay);
-
}
-
-
void flush_scheduled_work(void)
-
{
-
flush_workqueue(keventd_wq);
-
}
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