Re: [PATCH v9 03/11] btrfs: add support for inserting raid stripe extents

[Geert Uytterhoeven]

	Hi David,

On Thu, 14 Sep 2023, David Sterba wrote:
> On Thu, Sep 14, 2023 at 09:06:58AM -0700, Johannes Thumshirn wrote:
> > Add support for inserting stripe extents into the raid stripe tree on
> > completion of every write that needs an extra logical-to-physical
> > translation when using RAID.
> >
> > Inserting the stripe extents happens after the data I/O has completed,
> > this is done to a) support zone-append and b) rule out the possibility of
> > a RAID-write-hole.
> >
> > Signed-off-by: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>

> > --- /dev/null
> > +++ b/fs/btrfs/raid-stripe-tree.c
> > +static int btrfs_insert_striped_mirrored_raid_extents(
> > +				      struct btrfs_trans_handle *trans,
> > +				      struct btrfs_ordered_extent *ordered,
> > +				      u64 map_type)
> > +{
> > +	struct btrfs_io_context *bioc;
> > +	struct btrfs_io_context *rbioc;
> > +	const int nstripes = list_count_nodes(&ordered->bioc_list);
> > +	const int index = btrfs_bg_flags_to_raid_index(map_type);
> > +	const int substripes = btrfs_raid_array[index].sub_stripes;
> > +	const int max_stripes =
> > +		trans->fs_info->fs_devices->rw_devices / substripes;
>
> This will probably warn due to u64/u32 division.

Worse, it causes link failures in linux-next, as e.g. reported by
noreply@xxxxxxxxxxxxxx:

    ERROR: modpost: "__udivdi3" [fs/btrfs/btrfs.ko] undefined!

So despite being aware of the issue, you still queued it?

The use of "int" for almost all variables is also a red flag:
  - list_count_nodes() returns size_t,
  - btrfs_bg_flags_to_raid_index() returns an enum.
  - btrfs_raid_array[index].sub_stripes is u8,
  - The result of the division may not fit in 32-bit.

Thanks for fixing, soon! ;-)

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds