-----Original Message----- From: Maximilian Heyne mheyne@amazon.de Sent: Thursday, February 15, 2024 9:20 PM Cc: ravib@amazon.com; Maximilian Heyne mheyne@amazon.de; stable@vger.kernel.org; Theodore Ts'o tytso@mit.edu; Andreas Dilger adilger.kernel@dilger.ca; Yongqiang Yang xiaoqiangnk@gmail.com; linux-ext4@vger.kernel.org; linux-kernel@vger.kernel.org Subject: [External] : [PATCH v2] ext4: fix corruption during on-line resize
We observed a corruption during on-line resize of a file system that is larger than 16 TiB with 4k block size. With having more then 2^32 blocks resize_inode is turned off by default by mke2fs. The issue can be reproduced on a smaller file system for convenience by explicitly turning off resize_inode. An on-line resize across an 8 GiB boundary (the size of a meta block group in this setup) then leads to a corruption:
dev=/dev/<some_dev> # should be >= 16 GiB mkdir -p /corruption /sbin/mke2fs -t ext4 -b 4096 -O ^resize_inode $dev $((2 * 2**21 - 2**15)) mount -t ext4 $dev /corruption
dd if=/dev/zero bs=4096 of=/corruption/test count=$((2*2**21 - 4*2**15)) sha1sum /corruption/test # 79d2658b39dcfd77274e435b0934028adafaab11 /corruption/test
/sbin/resize2fs $dev $((2*2**21)) # drop page cache to force reload the block from disk echo 1 > /proc/sys/vm/drop_caches
sha1sum /corruption/test # 3c2abc63cbf1a94c9e6977e0fbd72cd832c4d5c3 /corruption/test
2^21 = 2^15*2^6 equals 8 GiB whereof 2^15 is the number of blocks per block group and 2^6 are the number of block groups that make a meta block group.
The last checksum might be different depending on how the file is laid out across the physical blocks. The actual corruption occurs at physical block 63*2^15 = 2064384 which would be the location of the backup of the meta block group's block descriptor. During the on-line resize the file system will be converted to meta_bg starting at s_first_meta_bg which is 2 in the example - meaning all block groups after 16 GiB. However, in ext4_flex_group_add we might add block groups that are not part of the first meta block group yet. In the reproducer we achieved this by substracting the size of a whole block group from the point where the meta block group would start. This must be considered when updating the backup block group descriptors to follow the non-meta_bg layout. The fix is to add a test whether the group to add is already part of the meta block group or not.
Fixes: 01f795f9e0d67 ("ext4: add online resizing support for meta_bg and 64-bit file systems") Cc: stable@vger.kernel.org
Tested the patch across filesystem of various sizes and blocksizes. The patch stops the corruption.
Signed-off-by: Maximilian Heyne mheyne@amazon.de
Tested-by: Srivathsa Dara srivathsa.d.dara@oracle.com Reviewed-by: Srivathsa Dara srivathsa.d.dara@oracle.com
fs/ext4/resize.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c index 4d4a5a32e310..3c0d12382e06 100644 --- a/fs/ext4/resize.c +++ b/fs/ext4/resize.c @@ -1602,7 +1602,8 @@ static int ext4_flex_group_add(struct super_block *sb, int gdb_num = group / EXT4_DESC_PER_BLOCK(sb); int gdb_num_end = ((group + flex_gd->count - 1) / EXT4_DESC_PER_BLOCK(sb));
int meta_bg = ext4_has_feature_meta_bg(sb);
int meta_bg = ext4_has_feature_meta_bg(sb) &&gdb_num >= le32_to_cpu(es->s_first_meta_bg);-- 2.40.1
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