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Date:	Thu, 23 Feb 2012 13:03:41 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	ext4 development <linux-ext4@...r.kernel.org>
CC:	Lukáš Czerner <lczerner@...hat.com>
Subject: Re: [PATCH] libext2: clear BG_BLOCK_UNINIT in any group containing
 metadata

On 2/23/12 12:20 PM, Eric Sandeen wrote:
> Running a test like the m_uninit test runs:
> 
> # mke2fs -F -o Linux -O uninit_bg testfs 131072
> 
> results in groups which have blocks allocated for metadata, but
> which still have the BLOCK_UNINIT flag set:
> 
> Group 2: (Blocks 16385-24576) [INODE_UNINIT, BLOCK_UNINIT, ITABLE_ZEROED]
>   Checksum 0x17c2, unused inodes 2048
>   Block bitmap at 16385 (+0), Inode bitmap at 16386 (+1)
>   Inode table at 16387-16642 (+2)
> 
> however, e2fsck doesn't find this error - which seems like another bug.
> 
> Doing another test like this:
> 
> mkfs.ext4 -I 256 -b 4096 -N 256 -G 1 -g 256 /dev/loop0 1024
> mount /dev/loop0 /mnt/test
> mkdir /mnt/test/dir
> umount /mnt/test
> fsck.ext4 -fn /dev/loop0
> 
> does find the error on fsck, I think because BLOCK_UNINIT gets
> cleared, and the group isn't ignored at fsck time:
> 
> Free blocks count wrong for group #2 (253, counted=249).
> 
> In the first case, flex_bg is not set; in the 2nd it is set,
> but s_log_groups_per_flex == 0 (due to -G 1), so in neither
> case is flexbg_size set in ext2fs_allocate_group_table().
> 
> This leads to skipping the code which clears BLOCK_UNINIT after
> the metadata is allocated.
> 
> I think the fix is to unconditionally clear the BLOCK_UNINIT flag
> in whatever block group gets metadata allocated to it, as follows.

I guess that's not right after talking to adilger.  I have to punt
on this for now, though, other deadlines approach.  Testcases above
if anyone else wants to look.

-Eric

> the m_uninit test needs to be fixed up too, as does e2fsck it seems,
> to catch this error in the first place?
> 
> Sorry for the long commit message, if the patch looks right I can
> try to do better ;)
> 
> Signed-off-by: Eric Sandeen <sandeen@...hat.com>
> ---
> 
> diff --git a/lib/ext2fs/alloc_tables.c b/lib/ext2fs/alloc_tables.c
> index 9f3d4e0..3462e85 100644
> --- a/lib/ext2fs/alloc_tables.c
> +++ b/lib/ext2fs/alloc_tables.c
> @@ -88,6 +88,7 @@ errcode_t ext2fs_allocate_group_table(ext2_filsys fs, dgrp_t group,
>  	blk64_t		group_blk, start_blk, last_blk, new_blk, blk;
>  	dgrp_t		last_grp = 0;
>  	int		rem_grps = 0, flexbg_size = 0;
> +	dgrp_t		gr;
>  
>  	group_blk = ext2fs_group_first_block2(fs, group);
>  	last_blk = ext2fs_group_last_block2(fs, group);
> @@ -141,13 +142,13 @@ errcode_t ext2fs_allocate_group_table(ext2_filsys fs, dgrp_t group,
>  			return retval;
>  		ext2fs_mark_block_bitmap2(bmap, new_blk);
>  		ext2fs_block_bitmap_loc_set(fs, group, new_blk);
> +		gr = ext2fs_group_of_blk2(fs, new_blk);
> +		ext2fs_bg_flags_clear(fs, gr, EXT2_BG_BLOCK_UNINIT);
>  		if (flexbg_size) {
> -			dgrp_t gr = ext2fs_group_of_blk2(fs, new_blk);
>  			ext2fs_bg_free_blocks_count_set(fs, gr, ext2fs_bg_free_blocks_count(fs, gr) - 1);
>  			ext2fs_free_blocks_count_add(fs->super, -1);
> -			ext2fs_bg_flags_clear(fs, gr, EXT2_BG_BLOCK_UNINIT);
> -			ext2fs_group_desc_csum_set(fs, gr);
>  		}
> +		ext2fs_group_desc_csum_set(fs, gr);
>  	}
>  
>  	if (flexbg_size) {
> @@ -172,13 +173,13 @@ errcode_t ext2fs_allocate_group_table(ext2_filsys fs, dgrp_t group,
>  			return retval;
>  		ext2fs_mark_block_bitmap2(bmap, new_blk);
>  		ext2fs_inode_bitmap_loc_set(fs, group, new_blk);
> +		gr = ext2fs_group_of_blk2(fs, new_blk);
> +		ext2fs_bg_flags_clear(fs, gr, EXT2_BG_BLOCK_UNINIT);
>  		if (flexbg_size) {
> -			dgrp_t gr = ext2fs_group_of_blk2(fs, new_blk);
>  			ext2fs_bg_free_blocks_count_set(fs, gr, ext2fs_bg_free_blocks_count(fs, gr) - 1);
>  			ext2fs_free_blocks_count_add(fs->super, -1);
> -			ext2fs_bg_flags_clear(fs, gr, EXT2_BG_BLOCK_UNINIT);
> -			ext2fs_group_desc_csum_set(fs, gr);
>  		}
> +		ext2fs_group_desc_csum_set(fs, gr);
>  	}
>  
>  	/*
> @@ -209,14 +210,13 @@ errcode_t ext2fs_allocate_group_table(ext2_filsys fs, dgrp_t group,
>  		     j < fs->inode_blocks_per_group;
>  		     j++, blk++) {
>  			ext2fs_mark_block_bitmap2(bmap, blk);
> +			gr = ext2fs_group_of_blk2(fs, blk);
> +			ext2fs_bg_flags_clear(fs, gr, EXT2_BG_BLOCK_UNINIT);
>  			if (flexbg_size) {
> -				dgrp_t gr = ext2fs_group_of_blk2(fs, blk);
>  				ext2fs_bg_free_blocks_count_set(fs, gr, ext2fs_bg_free_blocks_count(fs, gr) - 1);
>  				ext2fs_free_blocks_count_add(fs->super, -1);
> -				ext2fs_bg_flags_clear(fs, gr,
> -						     EXT2_BG_BLOCK_UNINIT);
> -				ext2fs_group_desc_csum_set(fs, gr);
>  			}
> +			ext2fs_group_desc_csum_set(fs, gr);
>  		}
>  		ext2fs_inode_table_loc_set(fs, group, new_blk);
>  	}
> 
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