RE: [bug report] rbd unmap hangs after pausing and unpausing I/O

[Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>]

On Wed, 2025-09-24 at 13:51 +0200, Raphael Zimmer wrote:
> On 23.09.25 19:42, Viacheslav Dubeyko wrote:
> > Hi Raphael,
> > 
> > On Tue, 2025-09-23 at 12:38 +0200, Raphael Zimmer wrote:
> > > Hello,
> > > 
> > > I encountered an error with the kernel Ceph client (specifically using
> > > an RBD device) when pausing I/O on the cluster by setting and unsetting
> > > pauserd and pausewr flags. An error was seen with two different setups,
> > > which I believe is due to the same problem.
> > > 
> > 
> > Thanks a lot for the report. Could you please create the ticket in a tracker
> > system [1]?
> > 
> > > 1) When pausing and later unpausing I/O on the cluster, everything seems
> > > to work as expected until trying to unmap an RBD device from the kernel.
> > > In this case, the rbd unmap command hangs and also can't be killed. To
> > > get back to a normally working state, a system reboot is needed. This
> > > behavior was observed on different systems (Debian 12 and 13) and could
> > > also be reproduced with an installation of the mainline kernel (v6.17-rc6).
> > > 
> > > Steps to reproduce:
> > > - Connect kernel client to RBD device (rbd map)
> > > - Pause I/O on cluster (ceph osd pause)
> > > - Wait some time (3 minutes should be enough)
> > > - Unpause I/O on cluster
> > > - Try to unmap RBD device on client
> > > 
> > 
> > Do you have a script? Could you please share the sequence of commands that you
> > used in command line to reproduce the issue?
> > 
> > Have you created any folders/files before pause/unpause the I/O requests on
> > cluster?
> > How have you initiated the I/O operations before pausing the I/O requests on
> > cluster?
> > Have you observed any warnings, call traces, or crashes from CephFS kernel
> > client in system log when rbd unmap command hangs (usually, kernel complains if
> > something is hanging significant amount of time)?
> > 
> > Thanks,
> > Slava.
> > 
> 
> Hi Slava,
> 
> I haven't used CephFS. Only an RBD image.
> The behavior is completely independent of whether I initiate any I/O 
> operations on the RBD image or not. You can reproduce the behavior by 
> following the exact steps from above:
> - rbd map <image-name> for an arbitrary image on the client host
> - ceph osd pause on the cluster
> - after some time: ceph osd unpause on the cluster
> - rbd unmap <image-name> on the client host
> You don't need to do anything else in between.
> 
> Since Ilya has already identified the issue and will attempt to fix it, 
> do you still want me to create the ticket in the tracker system?
> 

Hi Raphael,

I believe it will be better to create the ticket, anyway. Because, we need to
gather all known issues in the tracker system. Potentially, we can receive a
similar report with the same issue in the future and it will be great to have
the ticket with clear explanation of symptoms and reproducing path. You can
assign the ticket directly on Ilya. He will be able to close the ticket after
the fix. 

Thanks,
Slava.