On Mon, Aug 14, 2023 at 09:25:54AM +0200, Christian Brauner wrote: > On Fri, Aug 11, 2023 at 08:58:01AM -0400, Kent Overstreet wrote: > > I don't see the justification for the delay - every cycle there's some > > amount of vfs/block layer refactoring that affects filesystems, the > > super work is no different. > > So, the reason is that we're very close to having the super code > massaged in a shape where bcachefs should be able to directly make use > of the helpers instead of having to pull in custom code at all. But not > all that work has made it. Well, bcachefs really isn't doing anything terribly unusual here; we're using sget() directly, same as btrfs, and we have to because we're both multi device filesystems. Jan's restructing of mount_bdev() got me thinking that it should be possible to do a mount_bdevs() that both btrfs and bcachefs could use - but we don't need to be blocked on that, sget()'s been a normal exported interface since forever. Somewhat related, I dropped this patch from my tree: block: Don't block on s_umount from __invalidate_super() https://evilpiepirate.org/git/bcachefs.git/commit/?h=bcachefs-v6.3&id=1dd488901bc025a61e1ce1a0f54999a2b221bd78 and instead, for now we're closing block devices later in the shutdown path like other filesystems do (after calling generic_shutdown_super(), not in put_super()). But now I've got some test failures, e.g. https://evilpiepirate.org/~testdashboard/c/040e910f7f316ea6273c895dcc026b9f1ad36a8e/xfstests.generic.604/log.br and since you guys are switching block device opens to use a real holder, I suspect you'll be seeing the same issue soon. The bug is that the mount appears to be gone - generic_shutdown_super() is finished - so as far as userspace can tell everything is shutdown and we should be able to start using the block device again, but the unmount path hasn't actually called blkdev_put() yet. So that patch I posted is one way to solve the self-deadlock from calling blkdev_put() where we really want to be calling it... not the prettiest way, but I think this is something we do need to get fixed.
