Hi,
Theodore Ts'o wrote on 07/05/2015 04:41:
> Commit 8f4d8558391: "ext4: fix lazytime optimization" was not a
> complete fix. In the case where the inode number is a multiple of 16,
> and we could still end up updating an inode with dirty timestamps
> written to the wrong inode on disk. Oops.
>
> This can be easily reproduced by using generic/005 with a file system
> with metadata_csum and lazytime enabled.
>
> Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
> fs/ext4/inode.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index e057c6f..4ad73d3 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4348,7 +4348,12 @@ static void ext4_update_other_inodes_time(struct super_block *sb,
> int inode_size = EXT4_INODE_SIZE(sb);
>
> oi.orig_ino = orig_ino;
> - ino = (orig_ino & ~(inodes_per_block - 1)) + 1;
> + /*
> + * Calculate the first inode in the inode table block. Inode
> + * numbers are one-based. That is, the first inode in a block
> + * (assuming 4k blocks and 256 byte inodes) is (n*16 + 1).
> + */
> + ino = ((orig_ino - 1) & ~(inodes_per_block - 1)) + 1;
> for (i = 0; i < inodes_per_block; i++, ino++, buf += inode_size) {
> if (ino == orig_ino)
> continue;
>
thank you very much for the explanation. Now I think I understand:
/*
* Calculate the first inode in the original inode's inode table
* block. Inode numbers are one-based. That is, the first inode
* in a block is one plus the next-lowest to (orig_ino - 1)
* integral multiple of inodes_per_block. This can be calculated
* efficiently by bit masking since inodes_per_block is a power
* of 2 (assuming 4k blocks and 256 byte inodes).
*/
Regards,
Jörg.
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