From: Sander Eikelenboom Subject: Re: [PATCH] ext4: fix the free blocks calculation for ext3 file systems w/ uninit_bg Date: Thu, 7 Jun 2012 16:01:16 +0200 Message-ID: <1511035441.20120607160116@eikelenboom.it> References: <1339077153-13212-1-git-send-email-tytso@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: Ext4 Developers List , stable@kernel.org, Kees Cook To: Theodore Ts'o Return-path: Received: from static.121.164.40.188.clients.your-server.de ([188.40.164.121]:35155 "EHLO smtp.eikelenboom.it" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932369Ab2FGOB2 (ORCPT ); Thu, 7 Jun 2012 10:01:28 -0400 In-Reply-To: <1339077153-13212-1-git-send-email-tytso@mit.edu> Sender: linux-ext4-owner@vger.kernel.org List-ID: Thursday, June 7, 2012, 3:52:33 PM, you wrote: > Ext3 filesystems that are converted to use as many ext4 file system > features as possible will enable uninit_bg to speed up e2fsck times. > These file systems will have a native ext3 layout of inode tables and > block allocation bitmaps (as opposed to ext4's flex_bg layout). > Unfortunately, in these cases, when first allocating a block in an > uninitialized block group, ext4 would incorrectly calculate the number > of free blocks in that block group, and then errorneously report that > the file system was corrupt: > EXT4-fs error (device vdd): ext4_mb_generate_buddy:741: group 30, 32254 clusters in bitmap, 32258 in gd > This problem can be reproduced via: > mke2fs -q -t ext4 -O ^flex_bg /dev/vdd 5g > mount -t ext4 /dev/vdd /mnt > fallocate -l 4600m /mnt/test > The problem was caused by a bone headed mistake in the check to see if a > particular metadata block was part of the block group. > Many thanks to Kees Cook for finding and bisecting the buggy commit > which introduced this bug (commit fd034a84e1, present since v3.2). > Reported-by: Sander Eikelenboom > Reported-by: Kees Cook > Signed-off-by: "Theodore Ts'o" > Cc: stable@kernel.org > Cc: Sander Eikelenboom > Cc: Kees Cook > --- > Note: I send to push this to Linus soon, preferably before 3.5-rc2, so > I'd appreciate any comments ASAP. Thanks!! Compiled it, turned uninit_bg back on, now copying some GB's worth of data to the FS. No problems so far... BTW: Is there any (real) advantage to recreate the FS using the ext4's flex_bg instead of converting the ext3 to ext4 and using ext3 uninit_bg ? -- Sander > fs/ext4/balloc.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c > index 99b6324..cee7812 100644 > --- a/fs/ext4/balloc.c > +++ b/fs/ext4/balloc.c > @@ -90,8 +90,8 @@ unsigned ext4_num_overhead_clusters(struct super_block *sb, > * unusual file system layouts. > */ > if (ext4_block_in_group(sb, ext4_block_bitmap(sb, gdp), block_group)) { > - block_cluster = EXT4_B2C(sbi, (start - > - ext4_block_bitmap(sb, gdp))); > + block_cluster = EXT4_B2C(sbi, > + ext4_block_bitmap(sb, gdp) - start); > if (block_cluster < num_clusters) > block_cluster = -1; > else if (block_cluster == num_clusters) { > @@ -102,7 +102,7 @@ unsigned ext4_num_overhead_clusters(struct super_block *sb, > > if (ext4_block_in_group(sb, ext4_inode_bitmap(sb, gdp), block_group)) { > inode_cluster = EXT4_B2C(sbi, > - start - ext4_inode_bitmap(sb, gdp)); > + ext4_inode_bitmap(sb, gdp) - start); > if (inode_cluster < num_clusters) > inode_cluster = -1; > else if (inode_cluster == num_clusters) { > @@ -114,7 +114,7 @@ unsigned ext4_num_overhead_clusters(struct super_block *sb, > itbl_blk = ext4_inode_table(sb, gdp); > for (i = 0; i < sbi->s_itb_per_group; i++) { > if (ext4_block_in_group(sb, itbl_blk + i, block_group)) { > - c = EXT4_B2C(sbi, start - itbl_blk + i); > + c = EXT4_B2C(sbi, itbl_blk + i - start); > if ((c < num_clusters) || (c == inode_cluster) || > (c == block_cluster) || (c == itbl_cluster)) > continue;