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

Luis Chamberlain
2025-04-14T22:19:35Z

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?

Luis