From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: Re: [PATCH v4] mtd: Do not corrupt backing device of device node inode Date: Fri, 14 May 2010 02:04:34 +0100 Message-ID: <1273799074.9999.653.camel@macbook.infradead.org> References: <1273074054-11849-1-git-send-email-kirill@shutemov.name> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Jan Kara , Alexander Viro , David Howells , Alexander Shishkin , Artem Bityutskiy , linux-mtd@lists.infradead.org, linux-fsdevel@vger.kernel.org, stable@kernel.org, linux-kernel@vger.kernel.org To: "Kirill A. Shutemov" Return-path: Received: from casper.infradead.org ([85.118.1.10]:58401 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753191Ab0ENBEp (ORCPT ); Thu, 13 May 2010 21:04:45 -0400 In-Reply-To: <1273074054-11849-1-git-send-email-kirill@shutemov.name> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, 2010-05-05 at 18:40 +0300, Kirill A. Shutemov wrote: > We cannot modify file->f_mapping->backing_dev_info, because it will corrupt > backing device of device node inode, since file->f_mapping is equal to > inode->i_mapping (see __dentry_open() in fs/open.c). > > Let's introduce separate inode for MTD device with appropriate backing > device. I hate the fact that we have to do this -- is it really the only option? Is it _just_ for the backing_device_info? Can't that be done differently? > @@ -85,11 +88,27 @@ static int mtd_open(struct inode *inode, struct file *file) > goto out; > } > > - if (mtd->backing_dev_info) > - file->f_mapping->backing_dev_info = mtd->backing_dev_info; > + if (!mtd->inode) { > + mtd->inode = new_inode(mtd_inode_mnt->mnt_sb); I believe that would be a race condition, if it wasn't for the BKL. And what happens when you close the chardevice and call iput() on the inode so it's destroyed, and then you re-open the device? You never set mtd->inode = NULL, so won't it now try to igrab a stale pointer? You won't have seen this in your testing unless you made it prune the icache between the close and open calls. -- David Woodhouse Open Source Technology Centre David.Woodhouse@intel.com Intel Corporation