Re: [PATCH] md/raid0: avoid RAID0 data corruption due to layout confusion.

[Song Liu]

On Wed, Sep 11, 2019 at 12:10 AM NeilBrown <ne...@suse.de> wrote:
>
> On Tue, Sep 10 2019, Guoqing Jiang wrote:
>
> > On 9/10/19 5:45 PM, Song Liu wrote:
> >>
> >>
> >>> On Sep 10, 2019, at 12:33 AM, NeilBrown <ne...@suse.de> wrote:
> >>>
> >>> On Mon, Sep 09 2019, Song Liu wrote:
> >>>
> >>>> Hi Neil,
> >>>>
> >>>>> On Sep 9, 2019, at 7:57 AM, NeilBrown <ne...@suse.de> wrote:
> >>>>>
> >>>>>
> >>>>> If the drives in a RAID0 are not all the same size, the array is
> >>>>> divided into zones.
> >>>>> The first zone covers all drives, to the size of the smallest.
> >>>>> The second zone covers all drives larger than the smallest, up to
> >>>>> the size of the second smallest - etc.
> >>>>>
> >>>>> A change in Linux 3.14 unintentionally changed the layout for the
> >>>>> second and subsequent zones.  All the correct data is still stored, but
> >>>>> each chunk may be assigned to a different device than in pre-3.14 
> >>>>> kernels.
> >>>>> This can lead to data corruption.
> >>>>>
> >>>>> It is not possible to determine what layout to use - it depends which
> >>>>> kernel the data was written by.
> >>>>> So we add a module parameter to allow the old (0) or new (1) layout to 
> >>>>> be
> >>>>> specified, and refused to assemble an affected array if that parameter 
> >>>>> is
> >>>>> not set.
> >>>>>
> >>>>> Fixes: 20d0189b1012 ("block: Introduce new bio_split()")
> >>>>> cc: sta...@vger.kernel.org (3.14+)
> >>>>> Signed-off-by: NeilBrown <ne...@suse.de>
> >>>>
> >>>> Thanks for the patches. They look great. However, I am having problem
> >>>> apply them (not sure whether it is a problem on my side). Could you
> >>>> please push it somewhere so I can use cherry-pick instead?
> >>>
> >>> I rebased them on block/for-next, fixed the problems that Guoqing found,
> >>> and pushed them to
> >>>   https://github.com/neilbrown/linux md/raid0
> >>>
> >>> NeilBrown
> >>
> >> Thanks Neil!
> >
> > Thanks for the explanation about set the flag.
> >
> >>
> >> Guoqing, if this looks good, please reply with your Reviewed-by
> >> or Acked-by.
> >
> > No more comments from my side, but I am not sure if it is better/possible 
> > to use one
> > sysfs node to control the behavior instead of module parameter, then we can 
> > support
> > different raid0 layout dynamically.
>
> A strength of module parameters is that you can set them in
>   /etc/modprobe.d/00-local.conf
> and then they are automatically set on boot.
> For sysfs, you need some tool to set them.
>
> >
> > Anyway, Acked-by: Guoqing Jiang <guoqing.ji...@cloud.ionos.com>
> >

I am adding the following change to the 1/2. Please let me know if it doesn't
make sense.

Thanks,
Song

diff --git i/drivers/md/raid0.c w/drivers/md/raid0.c
index a9fcff50bbfc..54d0064787a8 100644
--- i/drivers/md/raid0.c
+++ w/drivers/md/raid0.c
@@ -615,6 +615,10 @@ static bool raid0_make_request(struct mddev
*mddev, struct bio *bio)
        case RAID0_ALT_MULTIZONE_LAYOUT:
                tmp_dev = map_sector(mddev, zone, sector, &sector);
                break;
+       default:
+               WARN("md/raid0:%s: Invalid layout\n", mdname(mddev));
+               bio_io_error(bio);
+               return true;
        }

        if (unlikely(is_mddev_broken(tmp_dev, "raid0"))) {