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Date:   Sat, 20 Oct 2018 06:05:22 +0100
From:   Al Viro <viro@ZenIV.linux.org.uk>
To:     David Howells <dhowells@redhat.com>
Cc:     linux-afs@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 03/24] iov_iter: Add I/O discard iterator
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On Sat, Oct 20, 2018 at 02:10:59AM +0100, David Howells wrote:

> @@ -1060,6 +1074,9 @@ void iov_iter_revert(struct iov_iter *i, size_t unroll)
>  	}
>  	unroll -= i->iov_offset;
>  	switch (iov_iter_type(i)) {
> +	case ITER_DISCARD:
> +		i->iov_offset = 0;
> +		return;

... the hell?  That makes no sense whatsoever; what, besides this and immediately
preceding part of iov_iter_revert() so much as looks at ->iov_offset for those?
Just have it bugger off before the
        if (unroll <= i->iov_offset) {
                i->iov_offset -= unroll;
                return;
        }
bit...