Re: [PATCH 1/2] btrfs-progs: check: run delayed refs after writing out dirty block groups

[Filipe Manana <fdmanana@gmail.com>]

On Wed, May 15, 2019 at 3:15 PM David Sterba <dsterba@suse.cz> wrote:
>
> On Wed, Apr 03, 2019 at 10:38:09PM -0400, Jeff Mahoney wrote:
> > On 4/2/19 3:19 PM, Filipe Manana wrote:
> > > On Tue, Apr 2, 2019 at 7:29 PM <jeffm@suse.com> wrote:
> > >>
> > >> From: Jeff Mahoney <jeffm@suse.com>
> > >>
> > >> When repairing the extent tree, it's possible for delayed extents to
> > >> be created when running btrfs_write_dirty_block_groups.  We run
> > >> delayed refs one last time in the kernel but that is missing in
> > >> the userspace tools.
> > >>
> > >> That results in delayed refs getting dropped on the floor, the extent
> > >> records not getting created, and in the next tranaction, when the
> > >> extent tree is CoW'd again, we hit the BUG_ON when we can't find
> > >> the extent record.
> > >>
> > >> We can fix this by running the delayed refs after writing out the
> > >> dirty block groups.
> > >>
> > >> Signed-off-by: Jeff Mahoney <jeffm@suse.com>
> > >> ---
> > >>  transaction.c | 2 ++
> > >>  1 file changed, 2 insertions(+)
> > >>
> > >> diff --git a/transaction.c b/transaction.c
> > >> index e756db33..2f19e9c8 100644
> > >> --- a/transaction.c
> > >> +++ b/transaction.c
> > >> @@ -194,6 +194,8 @@ commit_tree:
> > >>         ret = btrfs_run_delayed_refs(trans, -1);
> > >>         BUG_ON(ret);
> > >>         btrfs_write_dirty_block_groups(trans);
> > >> +       ret = btrfs_run_delayed_refs(trans, -1);
> > >> +       BUG_ON(ret);
> > >
> > > And running delayed refs can dirty more block groups as well.
> > > At this point shouldn't we loop running delayed refs until no more
> > > dirty block groups exist? Just like in the kernel.
> >
> > Right.  This is another argument for code sharing between the kernel and
> > userspace.
>
> Sharing code in this function would be really hard, I've implemented the
> loop in commit in progs.

Shouldn't the new patch version be sent to the list for review?
It doesn't seem to be a trivial change on first through.

Thanks.



-- 
Filipe David Manana,

“Whether you think you can, or you think you can't — you're right.”