Description of problem:


A snapshot deletion is executed on a RHV-M environment GUI for VM.

For a offline merge (VM down), in the vdsm logs of the host/hypervisor, the qemu-img commit fails with the following.

~~~
QImgError: cmd=['/usr/bin/taskset', '--cpu-list', '0-31', '/usr/bin/nice', '-n', '19', '/usr/bin/ionice', '-c', '3', '/usr/bin/qemu-img', 'commit', '-p', '-t', 'none', '-b', u'/rhev/data-center/mnt/glusterSD/EXAMPLE-gluster01_rhevm/ab27a13a-7a82-4cf4-86fd-3a6c697ccef9/images/3122bbad-e3d3-446a-90b9-eb6da08dad2a/7fa44a95-2988-4866-924c-329713989ad0', '-f', 'qcow2', u'/rhev/data-center/mnt/glusterSD/EXAMPLE-gluster01_rhevm/ab27a13a-7a82-4cf4-86fd-3a6c697ccef9/images/3122bbad-e3d3-446a-90b9-eb6da08dad2a/8ba82ba8-32ea-4501-95e8-55ef42812c89'], ecode=-6, stdout=, stderr=qemu-img: block/file-posix.c:1774: find_allocation: Assertion `offs >= start' failed.
, message=None
~~~

off_t offs;

~~~
    /*
     * SEEK_DATA cases:
     * D1. offs == start: start is in data
     * D2. offs > start: start is in a hole, next data at offs
     * D3. offs < 0, errno = ENXIO: either start is in a trailing hole
     *                              or start is beyond EOF
     *     If the latter happens, the file has been truncated behind
     *     our back since we opened it.  All bets are off then.
     *     Treating like a trailing hole is simplest.
     * D4. offs < 0, errno != ENXIO: we learned nothing
     */
    offs = lseek(s->fd, start, SEEK_DATA);
    if (offs < 0) {
        return -errno;          /* D3 or D4 */
    }
    assert(offs >= start)
~~~

The image resides on glusterfs.

This assertion failure seems similar to BZ 1451191, except that was relative to a gluster library function, glfs_lseek(), whereas in our case it's in lseek().

A live merge (VM online) fails with the following error:

~~~
libvirtError: internal error: child reported: Kernel does not provide mount namespace: No such file or directory
~~~

Journal logs, the qemu-kvm VM process aborts

~~~
Jan 03 09:53:34 EXAMPLE-host abrt-hook-ccpp[49478]: Process 48766 (qemu-kvm) of user 107 killed by SIGABRT - dumping core
Jan 03 09:53:34 EXAMPLE-host libvirtd[3141]: 2018-01-03 09:53:34.849+0000: 3141: error : qemuMonitorIORead:588 : Unable to read from monitor: Connection reset by peer
Jan 03 09:53:34 EXAMPLE-host libvirtd[3141]: 2018-01-03 09:53:34.853+0000: 3224: error : virProcessRunInMountNamespace:1159 : internal error: child reported: Kernel does not provide mount namespace: No such file or directory
Jan 03 09:53:34 EXAMPLE-host libvirtd[3141]: 2018-01-03 09:53:34.854+0000: 3224: error : virProcessRunInMountNamespace:1159 : internal error: child reported: Kernel does not provide mount namespace: No such file or directory
Jan 03 09:53:34 EXAMPLE-host libvirtd[3141]: 2018-01-03 09:53:34.937+0000: 3141: error : qemuAgentIO:652 : internal error: End of file from agent monitor
~~~

The images involved are:

~~~
u'top_id':  u'8ba82ba8-32ea-4501-95e8-55ef42812c89', 
u'base_id': u'7fa44a95-2988-4866-924c-329713989ad0'
~~~

The 8ba82ba8-32ea-4501-95e8-55ef42812c89 is a raw image and 7fa44a95-2988-4866-924c-329713989ad0 is cow

~~~
# su vdsm -s /bin/sh -c 'qemu-img check /rhev/data-center/mnt/glusterSD/EXAMPLE-gluster01_rhevm/ab27a13a-7a82-4cf4-86fd-3a6c697ccef9/images/3122bbad-e3d3-446a-90b9-eb6da08dad2a/8ba82ba8-32ea-4501-95e8-55ef42812c89'
Leaked cluster 17 refcount=1 reference=0

1 leaked clusters were found on the image.
This means waste of disk space, but no harm to data.
5983/327680 = 1.83% allocated, 12.32% fragmented, 0.00% compressed clusters
Image end offset: 393543680
~~~


Version-Release number of selected component (if applicable):

~~~
ovirt-engine-4.1.6.2-0.1.el7.noarch

Red Hat Virtualization Host 4.1 (el7.4) - 3.10.0-693.2.2.el7.x86_64

vdsm-4.19.31-1.el7ev.x86_64
qemu-kvm-rhev-2.9.0-16.el7_4.5.x86_64
libvirt-daemon-3.2.0-14.el7_4.3.x86_64
glusterfs-3.8.4-18.6.el7rhgs.x86_64
~~~


How reproducible:

100% on end user system.

Unable to reproduce on inhouse lab system.

Steps to Reproduce:
1.  With RHV delete a VM snapshot.  

2.
3.

Actual results:

Merge operation fails at qemu-img commit.

Expected results:

Operation should complete without error.

Additional info: