Messages in this thread | | | Date | Wed, 20 Sep 2023 07:20:49 +0930 | Subject | Re: [PATCH 1/4] btrfs: fix 64bit division in btrfs_insert_striped_mirrored_raid_extents | From | Qu Wenruo <> |
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On 2023/9/19 23:28, David Sterba wrote: > On Tue, Sep 19, 2023 at 10:07:00AM +0930, Qu Wenruo wrote: >> On 2023/9/19 01:54, David Sterba wrote: >>> On Mon, Sep 18, 2023 at 03:03:10PM +0000, Johannes Thumshirn wrote: >>>> On 18.09.23 16:19, Geert Uytterhoeven wrote: >>>>> Hi Johannes, >>>>> >>>>> On Mon, Sep 18, 2023 at 4:14 PM Johannes Thumshirn >>>>> <johannes.thumshirn@wdc.com> wrote: >>>>>> Fix modpost error due to 64bit division on 32bit systems in >>>>>> btrfs_insert_striped_mirrored_raid_extents. >>>>>> >>>>>> Cc: Geert Uytterhoeven <geert@linux-m68k.org> >>>>>> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com> >>>>> >>>>> Thanks for your patch! >>>>> >>>>>> --- a/fs/btrfs/raid-stripe-tree.c >>>>>> +++ b/fs/btrfs/raid-stripe-tree.c >>>>>> @@ -148,10 +148,10 @@ static int btrfs_insert_striped_mirrored_raid_extents( >>>>>> { >>>>>> 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; >>>>>> + const size_t nstripes = list_count_nodes(&ordered->bioc_list); >>>>>> + const enum btrfs_raid_types index = btrfs_bg_flags_to_raid_index(map_type); >>>>>> + const u8 substripes = btrfs_raid_array[index].sub_stripes; >>>>>> + const int max_stripes = div_u64(trans->fs_info->fs_devices->rw_devices, substripes); >>>>> >>>>> What if the quotient does not fit in a signed 32-bit value? >>>> >>>> Then you've bought a lot of HDDs ;-) >>>> >>>> Jokes aside, yes this is theoretically correct. Dave can you fix >>>> max_stripes up to be u64 when applying? >>> >>> I think we can keep it int, or unsigned int if needed, we can't hit such >>> huge values for rw_devices. The 'theoretically' would fit for a machine >>> with infinite resources, otherwise the maximum number of devices I'd >>> expect is a few thousand. >> >> In fact, we already have an check in btrfs_validate_super(), if the >> num_devices is over 1<<31, we would reject the fs. > > No, it's just a warning in that case.
We can make it a proper reject.
> >> I think we should be safe to further reduce the threshold. >> >> U16_MAX sounds a valid and sane value to me. >> If no rejection I can send out a patch for this. >> >> And later change internal rw_devices/num_devices to u16. > > U16 does not make sense here, it's not a native int type on many > architectures and generates awkward assembly code. We use it in > justified cases where it's saving space in structures that are allocated > thousand times. The arbitrary limit 65536 is probably sane but not > much different than 1<<31, practically not hit and was useful to > note fuzzed superblocks.
OK, we can make it unsigned int (mostly u32) for fs_info::*_devices, but still do extra limits on things like device add to limit it to U16_MAX.
Would this be a better solution? At least it would still half the width while keep it native to most (if not all) archs.
Thanks, Qu
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