Re: [PATCH v2 1/8] migrate: fix skipping metadata buffer heads on migration

Christian Brauner
2025-04-15T09:05:46Z

On Mon, Apr 14, 2025 at 03:19:33PM -0700, Luis Chamberlain wrote:
> On Mon, Apr 14, 2025 at 02:09:46PM -0700, Luis Chamberlain wrote:
> > On Thu, Apr 10, 2025 at 02:05:38PM +0200, Jan Kara wrote:
> > > > @@ -859,12 +862,12 @@ static int __buffer_migrate_folio(struct address_space *mapping,
> > > > }
> > > > bh = bh->b_this_page;
> > > > } while (bh != head);
> > > > + spin_unlock(&mapping->i_private_lock);
> > >
> > > No, you've just broken all simple filesystems (like ext2) with this patch.
> > > You can reduce the spinlock critical section only after providing
> > > alternative way to protect them from migration. So this should probably
> > > happen at the end of the series.
> >
> > So you're OK with this spin lock move with the other series in place?
> >
> > And so we punt the hard-to-reproduce corruption issue as future work
> > to do? Becuase the other alternative for now is to just disable
> > migration for jbd2:
> >
> > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > index 1dc09ed5d403..ef1c3ef68877 100644
> > --- a/fs/ext4/inode.c
> > +++ b/fs/ext4/inode.c
> > @@ -3631,7 +3631,6 @@ static const struct address_space_operations ext4_journalled_aops = {
> > .bmap = ext4_bmap,
> > .invalidate_folio = ext4_journalled_invalidate_folio,
> > .release_folio = ext4_release_folio,
> > - .migrate_folio = buffer_migrate_folio_norefs,
> > .is_partially_uptodate = block_is_partially_uptodate,
> > .error_remove_folio = generic_error_remove_folio,
> > .swap_activate = ext4_iomap_swap_activate,
>
> BTW I ask because.. are your expectations that the next v3 series also
> be a target for Linus tree as part of a fix for this spinlock
> replacement?

Since this is fixing potential filesystem corruption I will upstream
whatever we need to do to fix this. Ideally we have a minimal fix to
upstream now and a comprehensive fix and cleanup for v6.16.