I had this problem occasionally in a cluster where we were regularly mapping RBDs with KRBD. Something else we saw was that after this happened for un-mapping RBDs, was that it would start preventing mapping some RBDs as well. We were able to use strace and kill the sub-thread that was stuck to allow the RBD to finish un-mapping, but as it turned out, the server would just continue to hang on KRBD functions until the server was restarted. The kernel just seemed to be in a bad state and the 6 different kernels we tried were all affected the same way.
We switched to using rbd-fuse to get away from KRBD problems like this, but rbd-fuse came with its own problems.
On Wed, Jul 5, 2017 at 1:56 PM Stanislav Kopp <staskopp@xxxxxxxxx> wrote:
Hello,
I have problem that sometimes I can't unmap rbd device, I get "sysfs
write failed rbd: unmap failed: (16) Device or resource busy", there
is no open files and "holders" directory is empty. I saw on the
mailling list that you can "force" unmapping the device, but I cant
find how does it work. "man rbd" only mentions "force" as "KERNEL RBD
(KRBD) OPTION", but "modinfo rbd" doesn't show this option. Did I miss
something?
As client where rbd is mapped I use Debian stretch with kernel 4.9,
ceph cluster is on version 11.2.
Thanks,
Stan
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