Return-Path: linux-nfs-owner@vger.kernel.org Received: from bombadil.infradead.org ([198.137.202.9]:47854 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750704AbaLOQ4T (ORCPT ); Mon, 15 Dec 2014 11:56:19 -0500 Date: Mon, 15 Dec 2014 08:56:15 -0800 From: Christoph Hellwig To: Jan Kara Cc: Omar Sandoval , Alexander Viro , Andrew Morton , Trond Myklebust , Christoph Hellwig , David Sterba , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/8] swap: lock i_mutex for swap_writepage direct_IO Message-ID: <20141215165615.GA19041@infradead.org> References: <20141215162705.GA23887@quack.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20141215162705.GA23887@quack.suse.cz> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Mon, Dec 15, 2014 at 05:27:05PM +0100, Jan Kara wrote: > On Sun 14-12-14 21:26:56, Omar Sandoval wrote: > > The generic write code locks i_mutex for a direct_IO. Swap-over-NFS > > doesn't grab the mutex because nfs_direct_IO doesn't expect i_mutex to > > be held, but most direct_IO implementations do. > I think you are speaking about direct IO writes only, aren't you? For DIO > reads we don't hold i_mutex AFAICS. And also for DIO writes we don't > necessarily hold i_mutex - see for example XFS which doesn't take i_mutex > for direct IO writes. It uses it's internal rwlock for this (see > xfs_file_dio_aio_write()). So I think this is just wrong. The problem is that the use of ->direct_IO by the swap code is a gross layering violation. ->direct_IO is a callback for the filesystem, and the swap code need to call ->read_iter instead of ->readpage and ->write_tier instead of ->direct_IO, and leave the locking to the filesystem.