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

[Luis Chamberlain <mcgrof@kernel.org>]

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,