Answering to myself: It looks like ext4 lazy init does not play well with loop device.
If the ext4 filesystem was previously created with lazy init there are I/O errors. Disabling lazy init fixes problem. Bug or feature? Thanks,
I'm mounting an ext4 filesystem residing on an AHCI SATA disk via loop: losetup -o 64424509440 --sizelimit 34359738368 /dev/loop0 /dev/sda mount -t ext4 /dev/loop0 /mnt Works perfectly on <= 4.4.155 (latest version on 4.4.x longterm branch) On 4.9.126 (longterm branch) I get these errors: blk_update_request: I/O error, /dev/loop0, sector 23778144