Re: [PATCH 08/13] workqueue: add lock_pool_executing_work()

Lai Jiangshan
2013-02-05T12:15:35Z

于 2013/2/5 5:34, Tejun Heo 写道:
> Hello,
>
> On Fri, Feb 01, 2013 at 02:41:31AM +0800, Lai Jiangshan wrote:
>> +static struct worker_pool *lock_pool_executing_work(struct work_struct *work,
>> + struct worker **worker)
>> +{
>> + unsigned long pool_id = offq_work_pool_id(work);
>> + struct worker_pool *pool;
>> + struct worker *exec;
>> +
>> + if (pool_id == WORK_OFFQ_POOL_NONE)
>> + return NULL;
>> +
>> + pool = worker_pool_by_id(pool_id);
>> + if (!pool)
>> + return NULL;
>> +
>> + spin_lock(&pool->lock);
>> + exec = find_worker_executing_work(pool, work);
>> + if (exec) {
>> + BUG_ON(pool != exec->pool);
>> + *worker = exec;
>> + return pool;
>> + }
>> + spin_unlock(&pool->lock);
>> +
>> + return NULL;
>> +}
>
> So, if a work item is queued on the same CPU and it isn't being
> executed, it will lock, look up the hash, unlock and then lock again?
> If this is something improved by later patch, please explain so.
> There gotta be a better way to do this, right?
>

The caller can't call this function if the work is on queue.
the caller should call it only when CWQ bit is not set.

it is commentted "lock the pool a given offq work is running on",
sorry, comment is too short.