On Wed 09-07-25 13:49:12, Kent Overstreet wrote: > On Wed, Jul 09, 2025 at 07:23:07PM +0200, Jan Kara wrote: > > > It also avoids the problem of ->mark_dead events being generated > > > from a context that holds filesystem/vfs locks and then deadlocking > > > waiting for those locks to be released. > > > > > > IOWs, a multi-device filesystem should really be implementing > > > ->mark_dead itself, and should not be depending on being able to > > > lock the superblock to take an active reference to it. > > > > > > It should be pretty clear that these are not issues that the generic > > > filesystem ->mark_dead implementation should be trying to > > > handle..... > > > > Well, IMO every fs implementation needs to do the bdev -> sb transition and > > make sb somehow stable. It may be that grabbing s_umount and active sb > > reference is not what everybody wants but AFAIU btrfs as the second > > multi-device filesystem would be fine with that and for bcachefs this > > doesn't work only because they have special superblock instantiation > > behavior on mount for independent reasons (i.e., not because active ref > > + s_umount would be problematic for them) if I understand Kent right. > > So I'm still not fully convinced each multi-device filesystem should be > > shipping their special method to get from device to stable sb reference. > > Honestly, the sync_filesystem() call seems bogus. > > If the block device is truly dead, what's it going to accomplish? Notice that fs_bdev_mark_dead() calls sync_filesystem() only in case 'surprise' argument is false - meaning this is actually a notification *before* the device is going away. I.e., graceful device hot unplug when you can access the device to clean up as much as possible. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
