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

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Message-ID: <20141222073234.GA14207@mew>
Date:	Sun, 21 Dec 2014 23:32:34 -0800
From:	Omar Sandoval <osandov@...ndov.com>
To:	Al Viro <viro@...IV.linux.org.uk>
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 Sat, Dec 20, 2014 at 06:13:37AM +0000, Al Viro wrote:
> 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?

Ergh. I don't see why ->read_iter would be screwing around in the swap
cache or with the pages in the iterator, anything in particular you can
see happening?

-- 
Omar
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