From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Subject: Re: [PATCH 2/8] swap: lock i_mutex for swap_writepage direct_IO Date: Sat, 20 Dec 2014 06:51:33 +0000 Message-ID: <20141220065133.GC22149@ZenIV.linux.org.uk> References: <20141215162705.GA23887@quack.suse.cz> <20141215165615.GA19041@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jan Kara , Omar Sandoval , Andrew Morton , Trond Myklebust , David Sterba , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org To: Christoph Hellwig Return-path: Content-Disposition: inline In-Reply-To: <20141215165615.GA19041@infradead.org> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Mon, Dec 15, 2014 at 08:56:15AM -0800, Christoph Hellwig wrote: > 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. The thing is, ->read_iter() and ->write_iter() might decide to fall back to buffered IO path. XFS is unusual in that respect - there O_DIRECT ends up with short write in such case. Other filesystems, OTOH... -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org