linux-kernel - Re: [PATCH v2 4/5] swapfile: use ->read_iter and ->write

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Message-ID: <20141220061337.GB22149@ZenIV.linux.org.uk>
Date:	Sat, 20 Dec 2014 06:13:37 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Omar Sandoval <osandov@...ndov.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	Christoph Hellwig <hch@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH v2 4/5] swapfile: use ->read_iter and ->write_iter

On Fri, Dec 19, 2014 at 07:18:28PM -0800, Omar Sandoval wrote:

> +		ret = swap_file->f_op->read_iter(&kiocb, &to);
> +		if (ret == PAGE_SIZE) {
> +			SetPageUptodate(page);
>  			count_vm_event(PSWPIN);
> +			ret = 0;
> +		} else {
> +			ClearPageUptodate(page);
> +			SetPageError(page);
> +		}
> +		unlock_page(page);

Umm...  What's to guarantee that ->read_iter() won't try lock_page() on what
turns out to be equal to page?
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