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

Luis Chamberlain
2025-04-14T21:09:46Z

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,