linux-ext4 - Re: [PATCH v2 1/8] migrate: fix skipping metadata buffer heads on migration

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Message-ID: <Z_15mCAv6nsSgRTf@bombadil.infradead.org>
Date: Mon, 14 Apr 2025 14:09:44 -0700
From: Luis Chamberlain <mcgrof@...nel.org>
To: Jan Kara <jack@...e.cz>
Cc: brauner@...nel.org, tytso@....edu, adilger.kernel@...ger.ca,
	linux-ext4@...r.kernel.org, riel@...riel.com, dave@...olabs.net,
	willy@...radead.org, hannes@...xchg.org, oliver.sang@...el.com,
	david@...hat.com, axboe@...nel.dk, hare@...e.de,
	david@...morbit.com, djwong@...nel.org, ritesh.list@...il.com,
	linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
	linux-mm@...ck.org, gost.dev@...sung.com, p.raghav@...sung.com,
	da.gomez@...sung.com,
	syzbot+f3c6fda1297c748a7076@...kaller.appspotmail.com
Subject: Re: [PATCH v2 1/8] migrate: fix skipping metadata buffer heads on
 migration

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,