Thanks! The patch looks good to me.
On Thu, Feb 2, 2012 at 5:05 PM, Lukas Czerner <lczerner@xxxxxxxxxx> wrote:
> When resizing file system in the way that the new size of the file
> system is still in the same group (no new groups are added), then we can
> hit a BUG_ON in ext4_alloc_group_tables()
>
> BUG_ON(flex_gd->count == 0 || group_data == NULL);
>
> because flex_gd->count is zero. The reason is the missing check for such
> case, so the code always extend the last group fully and then attempt to
> add more groups, but at that time n_blocks_count is actually smaller
> than o_blocks_count.
>
> It can be easily reproduced like this:
>
> mkfs.ext4 -b 4096 /dev/sda 30M
> mount /dev/sda /mnt/test
> resize2fs /dev/sda 50M
>
> Fix this by checking whether the resize happens within the singe group
> and only add that many blocks into the last group to satisfy user
> request. Then o_blocks_count == n_blocks_count and the resize will exit
> successfully without and attempt to add more groups into the fs.
>
> Also fix mixing together block number and blocks count which might be
> confusing and can easily lead to off-by-one errors (but it is actually
> not the case here since the two occurrence of this mix-up will cancel
> each other).
>
> Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx>
> Reported-by: Milan Broz <mbroz@xxxxxxxxxx>
> ---
> fs/ext4/resize.c | 14 ++++++++------
> 1 files changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
> index f9d948f..3fed79d 100644
> --- a/fs/ext4/resize.c
> +++ b/fs/ext4/resize.c
> @@ -1582,7 +1582,7 @@ int ext4_resize_fs(struct super_block *sb, ext4_fsblk_t n_blocks_count)
> ext4_fsblk_t o_blocks_count;
> ext4_group_t o_group;
> ext4_group_t n_group;
> - ext4_grpblk_t offset;
> + ext4_grpblk_t offset, add;
> unsigned long n_desc_blocks;
> unsigned long o_desc_blocks;
> unsigned long desc_blocks;
> @@ -1605,7 +1605,7 @@ int ext4_resize_fs(struct super_block *sb, ext4_fsblk_t n_blocks_count)
> return 0;
>
> ext4_get_group_no_and_offset(sb, n_blocks_count - 1, &n_group, &offset);
> - ext4_get_group_no_and_offset(sb, o_blocks_count, &o_group, &offset);
> + ext4_get_group_no_and_offset(sb, o_blocks_count - 1, &o_group, &offset);
>
> n_desc_blocks = (n_group + EXT4_DESC_PER_BLOCK(sb)) /
> EXT4_DESC_PER_BLOCK(sb);
> @@ -1634,10 +1634,12 @@ int ext4_resize_fs(struct super_block *sb, ext4_fsblk_t n_blocks_count)
> }
> brelse(bh);
>
> - if (offset != 0) {
> - /* extend the last group */
> - ext4_grpblk_t add;
> - add = EXT4_BLOCKS_PER_GROUP(sb) - offset;
> + /* extend the last group */
> + if (n_group == o_group)
> + add = n_blocks_count - o_blocks_count;
> + else
> + add = EXT4_BLOCKS_PER_GROUP(sb) - (offset + 1);
> + if (add > 0) {
> err = ext4_group_extend_no_check(sb, o_blocks_count, add);
> if (err)
> goto out;
> --
> 1.7.4.4
>
--
Best Wishes
Yongqiang Yang
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