Re: [PATCH v4 1/6] fs: enhance and rename shutdown() callback to remove_bdev()

Jan Kara
2025-07-11T14:20:31Z

On Thu 10-07-25 14:41:18, Kent Overstreet wrote:
> On Thu, Jul 10, 2025 at 03:10:04PM +0200, Jan Kara wrote:
> > 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.
>
> That doesn't seem to be hooked up to anything?

__del_gendisk()
if (!test_bit(GD_DEAD, &disk->state))
blk_report_disk_dead(disk, false);

Is the path which results in "surprise" to be false. I have to admit I
didn't check deeper into drivers whether this is hooked up properly but
del_gendisk() is a standard call to tear down a disk so it would seem so
from the first glance.

Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR