On Fri, 17 Aug 2012 21:24:08 -0400
Ed Cashin <ecas...@coraid.com> wrote:
> This patch makes the frames the aoe driver uses to track the
> relationship between bios and packets more flexible and detached, so
> that they can be passed to an "aoe_ktio" thread for completion of I/O.
>
> The frames are handled much like skbs, with a capped amount of
> preallocation so that real-world use cases are likely to run smoothly
> and degenerate gracefully even under memory pressure.
>
> Decoupling I/O completion from the receive path and serializing it in
> a process makes it easier to think about the correctness of the
> locking in the driver, especially in the case of a remote MAC address
> becoming unusable.
>
> ...
>
> +static int
> +kthread(void *vp)
> +{
> + struct ktstate *k;
> + DECLARE_WAITQUEUE(wait, current);
> + sigset_t blocked;
> + int more;
> +
> + k = vp;
> +#ifdef PF_NOFREEZE
PF_NOFREEZE can never be undefined.
> + current->flags |= PF_NOFREEZE;
> +#endif
> + set_user_nice(current, -10);
> + sigfillset(&blocked);
> + sigprocmask(SIG_BLOCK, &blocked, NULL);
> + flush_signals(current);
This is a kernel thread - it shouldn't need to fiddle with signals.
> + complete(&k->rendez);
That's odd. Why do a complete() before we even start? A code comment
is needed if this is indeed correct.
> + do {
> + __set_current_state(TASK_UNINTERRUPTIBLE);
I think this statement is simply unneeded.
> + spin_lock_irq(k->lock);
> + more = k->fn();
> + if (!more) {
> + add_wait_queue(k->waitq, &wait);
> + __set_current_state(TASK_INTERRUPTIBLE);
> + }
> + spin_unlock_irq(k->lock);
> + if (!more) {
> + schedule();
> + remove_wait_queue(k->waitq, &wait);
> + } else
> + cond_resched();
Here we can do a cond_resched() when in state TASK_INTERRUPTIBLE. Such
a schedule() will never return unless some other thread flips this task
into state TASK_RUNNING. But if another thread does that, we should
have been on that waitqueue!
It seems all confused and racy.
> + } while (!kthread_should_stop());
> + __set_current_state(TASK_RUNNING);
I don't think there's any path by which we can get here in any state
other than TASK_RUNNING.
> + complete(&k->rendez);
> + return 0;
> +}
This function might be a bit neater if it were to use
prepare_to_wait()/finish_wait().
> +static void
> +aoe_ktstop(struct ktstate *k)
> +{
> + kthread_stop(k->task);
> + wait_for_completion(&k->rendez);
> +}
> +
> +static int
> +aoe_ktstart(struct ktstate *k)
> +{
> + struct task_struct *task;
> +
> + init_completion(&k->rendez);
> + task = kthread_run(kthread, k, k->name);
> + if (task == NULL || IS_ERR(task))
> + return -EFAULT;
EFAULT makes no sense?
> + k->task = task;
> + wait_for_completion(&k->rendez);
> + init_completion(&k->rendez); /* for exit */
> + return 0;
> +}
>
> ...
>
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