4.4-stable review patch. If anyone has any objections, please let me know.
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From: Jan Kara jack@suse.cz
commit f96c3ac8dfc24b4e38fc4c2eba5fea2107b929d1 upstream.
When computing maximum size of filesystem possible with given number of group descriptor blocks, we forget to include s_first_data_block into the number of blocks. Thus for filesystems with non-zero s_first_data_block it can happen that computed maximum filesystem size is actually lower than current filesystem size which confuses the code and eventually leads to a BUG_ON in ext4_alloc_group_tables() hitting on flex_gd->count == 0. The problem can be reproduced like:
truncate -s 100g /tmp/image mkfs.ext4 -b 1024 -E resize=262144 /tmp/image 32768 mount -t ext4 -o loop /tmp/image /mnt resize2fs /dev/loop0 262145 resize2fs /dev/loop0 300000
Fix the problem by properly including s_first_data_block into the computed number of filesystem blocks.
Fixes: 1c6bd7173d66 "ext4: convert file system to meta_bg if needed..." Signed-off-by: Jan Kara jack@suse.cz Signed-off-by: Theodore Ts'o tytso@mit.edu Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/ext4/resize.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/fs/ext4/resize.c +++ b/fs/ext4/resize.c @@ -1928,7 +1928,8 @@ retry: le16_to_cpu(es->s_reserved_gdt_blocks); n_group = n_desc_blocks * EXT4_DESC_PER_BLOCK(sb); n_blocks_count = (ext4_fsblk_t)n_group * - EXT4_BLOCKS_PER_GROUP(sb); + EXT4_BLOCKS_PER_GROUP(sb) + + le32_to_cpu(es->s_first_data_block); n_group--; /* set to last group number */ }