Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756517AbZCRMDf (ORCPT ); Wed, 18 Mar 2009 08:03:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753399AbZCRMDU (ORCPT ); Wed, 18 Mar 2009 08:03:20 -0400 Received: from ns2.suse.de ([195.135.220.15]:34334 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752421AbZCRMDU (ORCPT ); Wed, 18 Mar 2009 08:03:20 -0400 Date: Wed, 18 Mar 2009 13:00:23 +0100 From: Nick Piggin To: Jan Kara Cc: LKML , linux-ext4@vger.kernel.org Subject: Re: [PATCH 3/4] fs: Avoid data corruption with blocksize < pagesize Message-ID: <20090318120022.GB14622@wotan.suse.de> References: <1237311235-13623-1-git-send-email-jack@suse.cz> <1237311235-13623-2-git-send-email-jack@suse.cz> <1237311235-13623-3-git-send-email-jack@suse.cz> <1237311235-13623-4-git-send-email-jack@suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1237311235-13623-4-git-send-email-jack@suse.cz> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2232 Lines: 56 On Tue, Mar 17, 2009 at 06:33:54PM +0100, Jan Kara wrote: > Assume the following situation: > Filesystem with blocksize < pagesize - suppose blocksize = 1024, > pagesize = 4096. File 'f' has first four blocks already allocated. > (line with "state:" contains the state of buffers in the page - m = mapped, > u = uptodate, d = dirty) > > process 1: process 2: > > write to 'f' bytes 0 - 1024 > state: |mud,-,-,-|, page dirty > write to 'f' bytes 1024 - 4096: > __block_prepare_write() maps blocks > state: |mud,m,m,m|, page dirty > we fail to copy data -> copied = 0 > block_write_end() does nothing > page gets unlocked > writepage() is called on the page > block_write_full_page() writes buffers with garbage > > This patch fixes the problem by skipping !uptodate buffers in > block_write_full_page(). > > CC: Nick Piggin > Signed-off-by: Jan Kara > --- > fs/buffer.c | 7 ++++++- > 1 files changed, 6 insertions(+), 1 deletions(-) > > diff --git a/fs/buffer.c b/fs/buffer.c > index 9f69741..22c0144 100644 > --- a/fs/buffer.c > +++ b/fs/buffer.c > @@ -1774,7 +1774,12 @@ static int __block_write_full_page(struct inode *inode, struct page *page, > } while (bh != head); > > do { > - if (!buffer_mapped(bh)) > + /* > + * Parallel write could have already mapped the buffers but > + * it then had to restart before copying in new data. We > + * must avoid writing garbage so just skip the buffer. > + */ > + if (!buffer_mapped(bh) || !buffer_uptodate(bh)) > continue; I don't quite see how this can happen. Further down in this loop, we do a test_clear_buffer_dirty(), which should exclude this I think? And marking the buffer dirty if it is not uptodate should be a bug. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/