Re: [PATCH -mm 3/3][AIO] - AIO completion signal notification

[Christoph Hellwig <hch@infradead.org>]

> +static long aio_setup_sigevent(struct kiocb *iocb,
> +			       struct sigevent __user *user_event)
> +{
> +	int error = 0;
> +	sigevent_t event;
> +	struct task_struct *target;
> +	unsigned long flags;
> +
> +	if (!access_ok(VERIFY_READ, user_event, sizeof(struct sigevent)))
> +		return -EFAULT;
> +
> +	if (copy_from_user(&event, user_event, sizeof (event)))
> +		return -EFAULT;

> +

> +
> +	/* Check for the SIGEV_NONE case */
> +	if (event.sigev_notify == SIGEV_NONE)
> +		return 0;
> +
> +	/* Setup the request completion notification parameters */
> +	iocb->ki_notify.notify = event.sigev_notify;
> +	iocb->ki_notify.signo = event.sigev_signo;
> +	iocb->ki_notify.value = event.sigev_value;
> +
> +	/* Now get the notification target */
> +	read_lock(&tasklist_lock);
> +
> +	if ((target = good_sigevent(&event))) {
> +
> +		spin_lock_irqsave(&target->sighand->siglock, flags);
> +
> +		if (!(target->flags & PF_EXITING)) {
> +			iocb->ki_notify.target = target;
> +
> +			spin_unlock_irqrestore(&target->sighand->siglock, flags);
> +

I don't think there's a need to have the siglock for checking PF_EXITING,
and I also don't see why you need it for the assignment to
iocb->ki_notify.target.  What is it intended to protect?

> +			/*
> +			 * Get a ref on the task. It is dropped in really_put_req()
> +			 * when we're done with the iocb, be it from the normal
> +			 * completion path, the cancellation path or an error path.
> +			 */
> +			if (iocb->ki_notify.notify == (SIGEV_SIGNAL|SIGEV_THREAD_ID))
> +				get_task_struct(target);
> +		} else {
> +			spin_unlock_irqrestore(&target->sighand->siglock, flags);
> +			error = -EINVAL;
> +		}
> +	} else
> +		error = -EINVAL;
> +
> +	read_unlock(&tasklist_lock);
> +
> +	if (!error) {
> +		/*
> +		 * Alloc a sigqueue for this request
> +		 *
> +		 * NOTE: we cannot free the sigqueue in the completion path as
> +		 * the signal may not have been delivered to the target task.
> +		 * Therefore it has to be freed in __sigqueue_free() when the
> +		 * signal is collected if si_code is SI_ASYNCIO.
> +		 */
> +		if (unlikely(!(iocb->ki_sigq = sigqueue_alloc())))
> +			error =  -EAGAIN;

We leak the task reference here.

All in all aio_setup_sigevent is a big mess and the style is very odd.
It's also overcommented on what's beeing done instead of why.
I've attached an draft on how it should look like below.

> +	/* handle setting up the sigevent for POSIX AIO signals */
> +	req->ki_notify.notify = SIGEV_NONE;
> +
> +	if (iocb->aio_sigeventp) {
> +		ret = aio_setup_sigevent(req,
> +				     (struct sigevent __user *)(unsigned long)
> +				     iocb->aio_sigeventp);
> +		if (ret)
> +			goto out_put_req;
> +	}
> +
>  	ret = aio_setup_iocb(req);
>  
>  	if (ret)
> @@ -1610,6 +1729,10 @@ int fastcall io_submit_one(struct kioctx
>  	return 0;
>  
>  out_put_req:
> +	/* Undo the sigqueue alloc if someting went bad */
> +	if (req->ki_sigq)
> +		sigqueue_free(req->ki_sigq);
> +

Please put this after a separate label, so only callers after
aio_setup_sigevent try to check ki_sigq.



static long aio_setup_sigevent(struct kiocb *iocb,
			       struct sigevent __user *user_event)
{
	sigevent_t event;
	struct task_struct *target;
	unsigned long flags;

	if (copy_from_user(&event, user_event, sizeof (event)))
		return -EFAULT;

	if (event.sigev_notify == SIGEV_NONE)
		return 0;

	iocb->ki_notify.notify = event.sigev_notify;
	iocb->ki_notify.signo = event.sigev_signo;
	iocb->ki_notify.value = event.sigev_value;

	read_lock(&tasklist_lock);
	target = good_sigevent(&event);
	if (unlikely(!target || (target->flags & PF_EXITING)))
		goto out_unlock;
	iocb->ki_notify.target = target;

	if (iocb->ki_notify.notify == (SIGEV_SIGNAL|SIGEV_THREAD_ID)) {
		/*
		 * This reference will be dropped when we're done with
		 * the request.
		 */
		get_task_struct(target);
	}
	read_unlock(&tasklist_lock);

	/*
	 * NOTE: we cannot free the sigqueue in the completion path as
	 * the signal may not have been delivered to the target task.
	 * Therefore it has to be freed in __sigqueue_free() when the
	 * signal is collected if si_code is SI_ASYNCIO.
	 */
	iocb->ki_sigq = sigqueue_alloc();
	if (unlikely(!iocb->ki_sigq)) {
		put_task_struct(target);
		return -EAGAIN;
	}

	return 0;
 out_unlock:
	read_unlock(&tasklist_lock);
	return -EINVAL;
}