[DRBD-user] drbd-9.0.18-1 : BUG: unable to handle kernel NULL pointer dereference at 00000000000000b0

[Joel Colledge]

Hi Rob,

This is strange, since the filesystem DAX access uses essentially the same
checks as DRBD does. You can get more detail about the failure by doing the
mount test again after enabling the relevant debug logging as follows:
echo "file drivers/dax/super.c +p" > /sys/kernel/debug/dynamic_debug/control

Perhaps there is a subtle difference in the checks that DRBD does which is
relevant for your device on this kernel.

Best regards,
Joel


On Wed, Jun 12, 2019 at 8:04 AM Rob van der Wal <rob.vanderwal at surfsara.nl>
wrote:

> Hi Joel,
>
> Yes, I can mount with "-o dax":
>
> lvcreate -L 40G -n test-lv  vg_ssd
>   scan_dev_close /dev/sdb2 no DEV_IN_BCACHE set
>   Logical volume "test-lv" created.
> mkfs.ext4 -b 4K /dev/vg_ssd/test-lv
> mount -o dax /dev/vg_ssd/test-lv /mnt
> df /mnt
> Filesystem                  1K-blocks  Used Available Use% Mounted on
> /dev/mapper/vg_ssd-test--lv  41022688 49176  38859976   1% /mnt
>
> But it shows a failure in syslog:
> [518270.833954] EXT4-fs (dm-16): DAX enabled. Warning: EXPERIMENTAL, use
> at your own risk
> [518270.833959] EXT4-fs (dm-16): DAX unsupported by block device. Turning
> off DAX.
> [518270.835599] EXT4-fs (dm-16): mounted filesystem with ordered data
> mode. Opts: dax
>
> Regards,
> Rob
>
>
> On 6/11/19 3:57 PM, Joel Colledge wrote:
>
> Hi Rob,
>
> This is strange. It seems that your LV is reporting that it supports
> PMEM/DAX. I suggest that you check that this issue also occurs without
> DRBD. For example, create a filesystem and try to mount it with DAX
> enabled:
> mkfs.ext4 -b 4K /dev/<your-lv>
> mount -o dax /dev/<your-lv> <somewhere>
>
> The check the syslog to see whether DAX was successfully enabled. You
> can see the expected success and failure output here:https://nvdimm.wiki.kernel.org/#filesystems
>
> Best regards,
> Joel
>
> PS Please "reply all" to keep the mailing list in CC
>
>
> On Tue, Jun 11, 2019 at 2:53 PM Rob van der Wal<rob.vanderwal at surfsara.nl> <rob.vanderwal at surfsara.nl> wrote:
>
> Hi Joel,
>
> I've build the module from source (downloaded from https://www.linbit.com/en/drbd-community/drbd-download/).
>
> I think we don't use external metadata and we are using a ssd disk for storing. This is a part of our drbd.conf:
> drbd.conf:
>     on barentsz {
>         node-id 1;
>         device           /dev/drbd0 minor 0;
>         disk             /dev/vg_ssd/vm_prace-ldap;
>         meta-disk        internal;
>         address          ipv4 10.0.0.30:7788;
>     }
>
>
> LVM info:
>   PV /dev/sdb2   VG vg_ssd          lvm2 [446.43 GiB / 102.43 GiB free]
>   ACTIVE            '/dev/vg_ssd/vm_prace-ldap' [38.00 GiB] inherit
>
> The requested line in the syslog is:
> [1037978.736262] drbd r0/0 drbd0: meta-data IO uses: dax-pmem
>
> But I don't think we are using a PMEM device so this looks not correct.
>
> Regards,
> Rob van der Wal
>
>
>
> --
> Rob van der Wal
> Supercomputing | SURFsara | Science Park 140 | 1098 XG Amsterdam | T +31
> 20 800  1300 | Rob.vanderWal at surfsara.nl | www.surfsara.nl |
>
>             We are ISO 27001 certified and meet the high requirements for
> information security.
>


-- 
Joel Colledge - Software Developer
+43-1-817-82-92 x53 <+4318178292>
joel.colledge at linbit.com

LIN <http://www.linbit.com/en/>BIT <http://www.linbit.com/en/> | Keeping
the Digital World Running
DRBD HA - Disaster Recovery - Software-defined Storage
t <https://twitter.com/linbit> / f
<https://www.facebook.com/pg/linbitdrbd/posts/> / in
<https://www.linkedin.com/company/linbit> / y
<https://www.youtube.com/user/linbit> / g+
<https://plus.google.com/+Linbit/about>

DRBD® and LINBIT® are registered trademarks of LINBIT, Austria.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.linbit.com/pipermail/drbd-user/attachments/20190612/b059777c/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: SURFsara
Type: image/png
Size: 2515 bytes
Desc: not available
URL: <http://lists.linbit.com/pipermail/drbd-user/attachments/20190612/b059777c/attachment.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: ISO27001
Type: image/png
Size: 1742 bytes
Desc: not available
URL: <http://lists.linbit.com/pipermail/drbd-user/attachments/20190612/b059777c/attachment-0001.png>