From: Jan Kara Subject: Re: [PATCH] ext4: ext4_split_extent shoult take care about extent zeroout Date: Thu, 31 Jan 2013 15:18:34 +0100 Message-ID: <20130131141834.GC4612@quack.suse.cz> References: <1359617098-18451-1-git-send-email-dmonakhov@openvz.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-ext4@vger.kernel.org, tytso@mit.edu, jack@suse.cz, xiaoqiangnk@gmail.com To: Dmitry Monakhov Return-path: Received: from cantor2.suse.de ([195.135.220.15]:40329 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750921Ab3AaOSq (ORCPT ); Thu, 31 Jan 2013 09:18:46 -0500 Content-Disposition: inline In-Reply-To: <1359617098-18451-1-git-send-email-dmonakhov@openvz.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Thu 31-01-13 11:24:58, Dmitry Monakhov wrote: > We have to update extent's state after first ext4_split_extent_at otherwise this result > in following trace: > ->ext4_ext_handle_uninitialized_extents (ex=[1000:20:uninit], lblock 1000, max_blocks 10) > ->ext4_split_extent_at(ex=[1000,128], lblk 10010) /// First split > ->ext4_ext_split() -> ENOSPC > ->ext4_ext_zeroout > ->ext4_ext_dirty -> ex=[1000:20:init] > ->ext4_split_extent_at(ex=[1000,128], lblk 10000) /// Second split > if(split == ee_block) > if (split_flag & EXT4_EXT_MARK_UNINIT2) > ext4_ext_mark_uninitialized(ex); ex=[1000:20:uninit] /// The bug! > ->ext4_ext_dirty ->ex=[1000:20:uninit] > > At the end ext4_convert_unwritten_extents_endio() will findout large uninitialized > extent. Thanks for debugging this. You fix look correct so you can add Reviewed-by: Jan Kara but I have to say the above changelog isn't optimal. I had to look into the code to verify you are actually speaking about what I think you are speaking. I think there are some mistakes in block numbers and notation for extents isn't comletely clear either. Can we make the changelog something like: When ext4_split_extent_at() ends up doing zeroout & conversion to initialized instead of split & conversion, ext4_split_extent() gets confused and can wrongly mark the extent back as uninitialized resulting in end IO code getting confused from large unwritten extents (it doesn't result in data corruption mostly by luck). The example of problematic behavior is: lblk len lblk len ext4_split_extent() (ex=[1000,30,uninit], map=[1010,10]) ext4_split_extent_at() (split [1000,30,uninit] at 1020) ext4_ext_insert_extent() -> ENOSPC ext4_ext_zeroout() -> extent [1000,30] is now initialized ext4_split_extent_at() (split [1000,30,init] at 1010, MARK_UNINIT1 | MARK_UNINIT2) -> extent is split and parts marked as uninitialized Fix the problem by rechecking extent type after the first ext4_split_extent_at() returns. --- What do you think? BTW: we don't have to further try to split the extent once it gets initialized do we? For now I'd keep your fix just to make ext4_split_extent() generic but noone really calls that function for initialized extent or is interested in splitting once the extent gets initialized. That code seriously needs some diet... Honza > > TESTCASE: https://github.com/dmonakhov/xfstests/commit/1a1c4f337d4d198803436c63a56625b1a78d8a5e > > Signed-off-by: Dmitry Monakhov > --- > fs/ext4/extents.c | 14 ++++++++++---- > 1 files changed, 10 insertions(+), 4 deletions(-) > > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c > index 97cac01..7a3f679 100644 > --- a/fs/ext4/extents.c > +++ b/fs/ext4/extents.c > @@ -3091,18 +3091,24 @@ static int ext4_split_extent(handle_t *handle, > if (err) > goto out; > } > - > + /* Update path is required because previous ext4_split_extent_at() may > + * result in split of original leaf or extent zeroout. > + */ Style nit comment should look like: /* * Update path is required because previous ext4_split_extent_at() may * result in split of original leaf or extent zeroout. */ > ext4_ext_drop_refs(path); > path = ext4_ext_find_extent(inode, map->m_lblk, path); > if (IS_ERR(path)) > return PTR_ERR(path); > + depth = ext_depth(inode); > + ex = path[depth].p_ext; > + uninitialized = ext4_ext_is_uninitialized(ex); > > if (map->m_lblk >= ee_block) { > split_flag1 = split_flag & EXT4_EXT_MAY_ZEROOUT; > - if (uninitialized) > + if (uninitialized) { > split_flag1 |= EXT4_EXT_MARK_UNINIT1; > - if (split_flag & EXT4_EXT_MARK_UNINIT2) > - split_flag1 |= EXT4_EXT_MARK_UNINIT2; > + if (split_flag & EXT4_EXT_MARK_UNINIT2) > + split_flag1 |= EXT4_EXT_MARK_UNINIT2; > + } > err = ext4_split_extent_at(handle, inode, path, > map->m_lblk, split_flag1, flags); > if (err) > -- > 1.7.1 > -- Jan Kara SUSE Labs, CR