Re: [PATCH v4 08/22] kthread: Initial support for delayed kthread work
From: Tejun Heo <hidden>
Date: 2016-01-25 19:05:01
Also in:
linux-mm, lkml
Hello, On Mon, Jan 25, 2016 at 04:44:57PM +0100, Petr Mladek wrote:
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+/* + * Returns true when there is a pending operation for this work. + * In particular, it checks if the work is: + * - queued + * - a timer is running to queue this delayed work + * + * This function must be called with locked work. + */ +static inline bool kthread_work_pending(const struct kthread_work *work) +{ + return !list_empty(&work->node) || + (work->timer && timer_active(work->timer)); +}
Why not just put the work item on a separate list so that lits_empty(&work->node) is always enough? IOW, put delayed work items on timers on worker->delayed or sth.
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+/* + * Queue @work right into the worker queue. + */ +static void __queue_kthread_work(struct kthread_worker *worker, + struct kthread_work *work) +{ + insert_kthread_work(worker, work, &worker->work_list); +}
Does this really need to be an inline function? This sort of one liner helpers tend to be obfuscating more than anything else.
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@@ -756,6 +779,121 @@ bool queue_kthread_work(struct kthread_worker *worker, } EXPORT_SYMBOL_GPL(queue_kthread_work); +static bool try_lock_kthread_work(struct kthread_work *work) +{ + struct kthread_worker *worker; + int ret = false; + +try_again: + worker = work->worker; + + if (!worker) + goto out;
return false;
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+ + spin_lock(&worker->lock); + if (worker != work->worker) { + spin_unlock(&worker->lock); + goto try_again; + }
return true;
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+ ret = true; + +out: + return ret; +}
Stop building unnecessary structures. Keep it simple.
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+static inline void unlock_kthread_work(struct kthread_work *work) +{ + spin_unlock(&work->worker->lock); +}
Ditto. Just open code it. It doesn't add anything.
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+/** + * delayed_kthread_work_timer_fn - callback that queues the associated delayed + * kthread work when the timer expires. + * @__data: pointer to the data associated with the timer + * + * The format of the function is defined by struct timer_list. + * It should have been called from irqsafe timer with irq already off. + */ +void delayed_kthread_work_timer_fn(unsigned long __data) +{ + struct delayed_kthread_work *dwork = + (struct delayed_kthread_work *)__data; + struct kthread_work *work = &dwork->work; + + if (!try_lock_kthread_work(work))
Can you please explain why try_lock is necessary here? That's the most important and non-obvious thing going on here and there's no explanation of that at all. Thanks. -- tejun