Hello! On Tue 24-10-23 16:53:38, Christian Brauner wrote: > This is a mechanism that allows the holder of a block device to yield > device access before actually closing the block device. > > If a someone yields a device then any concurrent opener claiming the > device exclusively with the same blk_holder_ops as the current owner can > wait for the device to be given up. Filesystems by default use > fs_holder_ps and so can wait on each other. > > This mechanism allows us to simplify superblock handling quite a bit at > the expense of requiring filesystems to yield devices. A filesytems must > yield devices under s_umount. This allows costly work to be done outside > of s_umount. > > There's nothing wrong with the way we currently do things but this does > allow us to simplify things and kills a whole class of theoretical UAF > when walking the superblock list. I'm not sure why is it better to create new ->yield callback called under sb->s_umount rather than just move blkdev_put() calls back into ->put_super? Or at least yielding could be done in ->put_super instead of a new callback if for some reason that is better than releasing the devices right away in ->put_super. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
