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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <tb55nsh7sscqq7x7qx2o6tc4gusv6uuledhldjmibi7ga5xgyq@d77ebe7r6s5d>
Date: Tue, 15 Apr 2025 13:23:00 +0200
From: Jan Kara <jack@...e.cz>
To: Luis Chamberlain <mcgrof@...nel.org>
Cc: Jan Kara <jack@...e.cz>, 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 Mon 14-04-25 14:09:44, 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?

Yes.

> And so we punt the hard-to-reproduce corruption issue as future work
> to do?

Yes, I'm not happy about that but I prefer that over putting band aids
into that code. Even more so because we don't even understand whether they
fix the problem or just make this reproducer stop working...

> 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,

This will not disable migration for JBD2 buffers. This will just disable
migration for files with data journalling. See my other reply for details.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR