From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kara Subject: Re: [PATCH] ext4: Unmap metadata when zeroing blocks Date: Mon, 3 Oct 2016 09:18:48 +0200 Message-ID: <20161003071848.GC6457@quack2.suse.cz> References: <1474992918-20488-1-git-send-email-jack@suse.cz> <20160929131457.wyhlp34n55ewzzxu@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jan Kara , Ted Tso , linux-ext4@vger.kernel.org To: Lukas Czerner Return-path: Received: from mx2.suse.de ([195.135.220.15]:45613 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751542AbcJCHSu (ORCPT ); Mon, 3 Oct 2016 03:18:50 -0400 Content-Disposition: inline In-Reply-To: <20160929131457.wyhlp34n55ewzzxu@localhost.localdomain> Sender: linux-ext4-owner@vger.kernel.org List-ID: Hi, On Thu 29-09-16 15:14:57, Lukas Czerner wrote: > do we have a xfstest case for this particular problem ? Not specifically, but some of the existing xfstests did trigger this problem for me which is how I found it out... Honza > On Tue, Sep 27, 2016 at 06:15:18PM +0200, Jan Kara wrote: > > When zeroing blocks for DAX allocations, we also have to unmap aliases > > in the block device mappings. Otherwise writeback can overwrite zeros > > with stale data from block device page cache. > > > > Signed-off-by: Jan Kara > > --- > > fs/ext4/inode.c | 10 +++++++++- > > 1 file changed, 9 insertions(+), 1 deletion(-) > > > > Ted, can you merge this patch please? It's a data corruption issue for DAX. > > > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c > > index c6ea25a190f8..87150122d361 100644 > > --- a/fs/ext4/inode.c > > +++ b/fs/ext4/inode.c > > @@ -647,11 +647,19 @@ found: > > /* > > * We have to zeroout blocks before inserting them into extent > > * status tree. Otherwise someone could look them up there and > > - * use them before they are really zeroed. > > + * use them before they are really zeroed. We also have to > > + * unmap metadata before zeroing as otherwise writeback can > > + * overwrite zeros with stale data from block device. > > */ > > if (flags & EXT4_GET_BLOCKS_ZERO && > > map->m_flags & EXT4_MAP_MAPPED && > > map->m_flags & EXT4_MAP_NEW) { > > + ext4_lblk_t i; > > + > > + for (i = 0; i < map->m_len; i++) { > > + unmap_underlying_metadata(inode->i_sb->s_bdev, > > + map->m_pblk + i); > > + } > > ret = ext4_issue_zeroout(inode, map->m_lblk, > > map->m_pblk, map->m_len); > > if (ret) { > > -- > > 2.6.6 > > > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Jan Kara SUSE Labs, CR