On Sat, 16 Mar 2024 20:26:15 +0200
Shaya Potter <spotter@xxxxxxxxx> wrote:
> note: not subscribed, so please cc me on responses.
>
> I recently had a Dell R710 die where I was using the Perc6 to provide
> storage to the box. As the box wasn't usable, I decided to image the
> individual disks to a newer machine with significantly more storage.
>
> I sort of messed up the progress, but that might have discovered a bug in
> mdadm.
>
> Background, the Dell R710 supported 6 drives, which I had as a 1TB
> SATA SSD and 5x8TB SATA disks in a RAID5 array.
>
> In the process of imaging it, I I was setting up devices on /dev/loop
> to be prepared to assemble the raid, but I think I accidentally
> assembled the raid while imaging the last disk (which in effect caused
> the last disk to get out of sync with the other disks. This was
> initially ok, until the VM I was doing it on, crashed with a KVM/QEMU
> failure (unsure what occurred).
>
> I was hoping, it was going to be easy to bring up the raid array
> again, but now mdadm was segfault on a null pointer exception whenever
> I tried to assemble the array (was just trying the RAID5 portion).
>
> I was thinking perhaps my VM got corrupted, but I couldn't figure that
> out, so I decided to try and reimage the disks (more carefully this
> time), but yes, the 5th disk was marked as in quick init, while the
> others were more consistent.
>
> Howvever, same segfault was occuring, so I built mdadm from source
> (with -g and no -O, as an aside, this would be a good Makefile target
> to have, to make issues easier to debug)
>
> After understanding the issue, the segfault seems to be due to
> Assemble.c wanting to call update_super() with a ddf super. Except
> super-ddf.c doesn't provide that.
>
> i.e. in Assemble.c it was crashing at
>
> if (st->ss->update_super(st, &devices[j].i, UOPT_SPEC_ASSEMBLE, NULL,
> c->verbose, 0, NULL)) {...}
>
> which now explained the seg fault on null pointer exception. I was
> able to progress past the segfault (perhaps badly, but it "seems" to
> work for me), by putting in a null check before the update_super()
> call, i.e.
>
> if (st->ss->update_super && st->ss->update_super(....)) { ... }
>
> thoughts about my "fix" (perhaps super-ddf.c needs an empty
> update_super function?) , if this is a bug? (perhaps its unexpected
> for me to have gotten into this state in the first place?)
>
Hello Shaya,
DDF is not actively developed. I'm considering dropping
it.
If you are interested in bringing it too life then you are
more than welcome to send patches!
If DDF doesn't implement update_super() then fix proposed by you seems to be
valid. Please send proper patch for that then we will review it.
Thanks,
Mariusz
