Re: [PATCH 1/4] Vectorize aio_read/aio_write methods

[Andrew Morton]

Badari Pulavarty <pbadari@xxxxxxxxxx> wrote:
>
>  static ssize_t ep_aio_read_retry(struct kiocb *iocb)
>  {
>  	struct kiocb_priv	*priv = iocb->private;
> -	ssize_t			status = priv->actual;
> +	ssize_t			len, total;
>  
>  	/* we "retry" to get the right mm context for this: */
> -	status = copy_to_user(priv->ubuf, priv->buf, priv->actual);
> -	if (unlikely(0 != status))
> -		status = -EFAULT;
> -	else
> -		status = priv->actual;
> +
> +	/* copy stuff into user buffers */
> +	total = priv->actual;
> +	len = 0;
> +	for (i=0; i < priv->count; i++) {
> +		ssize_t this = min(priv->iv[i].iov_len, total);
> +
> +		if (copy_to_user(priv->iv[i].iov_buf, priv->buf, this))
> +			break;
> +
> +		total -= this;
> +		len += this;
> +		if (total <= 0)
> +			break;
> +	}
> +
> +	if (unlikely(len == 0))
> +		len = -EFAULT;

This is still wrong, isn't it?  Or am I looking at the same patch?

There's no way in which `total' can go negative, so it'd be nicer to just
test it for equality with zero.  Because if it goes unexpectedly negative,
we _want_ the kernel to malfunction, rather than mysteriously covering
things up.

The final test there should be

	if (unlikely(total != 0))

yes?
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