On Tue 17-01-23 18:25:40, Darrick J. Wong wrote: > [add linux-xfs to cc on this one] > > On Fri, Jan 13, 2023 at 04:33:48PM -0800, Luis Chamberlain wrote: > > Userspace can initiate a freeze call using ioctls. If the kernel decides > > to freeze a filesystem later it must be able to distinguish if userspace > > had initiated the freeze, so that it does not unfreeze it later > > automatically on resume. > > Hm. Zooming out a bit here, I want to think about how kernel freezes > should behave... > > > Likewise if the kernel is initiating a freeze on its own it should *not* > > fail to freeze a filesystem if a user had already frozen it on our behalf. > > ...because kernel freezes can absorb an existing userspace freeze. Does > that mean that userspace should be prevented from undoing a kernel > freeze? Even in that absorption case? > > Also, should we permit multiple kernel freezes of the same fs at the > same time? And if we do allow that, would they nest like freeze used to > do? > > (My suggestions here are 'yes', 'yes', and '**** no'.) Yeah, makes sense to me. So I think the mental model to make things safe is that there are two flags - frozen_by_user, frozen_by_kernel - and the superblock is kept frozen as long as either of these is set. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
