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

Rob van der Wal rob.vanderwal at surfsara.nl
Wed Jun 12 08:04:56 CEST 2019

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


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> 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;
>>      }
>> 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 |

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