linux-kernel - Re: [PATCH 2/8] swap: lock i_mutex for swap_writepage direct

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Message-ID: <20141217082437.GA9301@infradead.org>
Date:	Wed, 17 Dec 2014 00:24:37 -0800
From:	Christoph Hellwig <hch@...radead.org>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Omar Sandoval <osandov@...ndov.com>, Jan Kara <jack@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	David Sterba <dsterba@...e.cz>, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-nfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/8] swap: lock i_mutex for swap_writepage direct_IO

On Wed, Dec 17, 2014 at 08:20:21AM +0000, Al Viro wrote:
> Where the hell would those other references come from?  We open the damn
> thing in sys_swapon(), never put it into descriptor tables, etc. and
> the only reason why we use filp_close() instead of fput() is that we
> would miss ->flush() otherwise.
> 
> Said that, why not simply *open* it with O_DIRECT to start with and be done
> with that?  It's not as if those guys came preopened by caller - swapon(2)
> gets a pathname and does opening itself.

Oops, should have dug deeper into the code.  For some reason I assumed
the fd is passed in from userspace.

The suggestion from Al is much better, given that we never do normal
I/O on the swapfile, just the bmap + direct bio submission which I hope
could go away in favor of the direct I/O variant in the long run.
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