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Created attachment 1456396 [details]
gdb_debug_info-07042018

Description of problem:
If use glusterfs as the storage backend, 'qemu-img commit' would 'Aborted (core dumped)'

# qemu-img commit -f qcow2 sn2
qemu-img: First cluster in emptied image is in use
Aborted (core dumped)


Version-Release number of selected component (if applicable):
Host kernel: 3.10.0-915.el7.x86_64
Qemu-kvm-rhev: qemu-kvm-rhev-2.12.0-6.el7.x86_64

How reproducible:
100%

Steps to Reproduce:
1. Mount gluestfs storage:
# mount -t glusterfs xx.xx.xx.xx:/gv1 /home

2. Create src image and its external snapshot on the glusterfs storage:
# cd /home
# qemu-img create -f qcow2 test 1G
# qemu-img create -f qcow2 test-sn -b test -F qcow2

3. Commit the snapshot to its base:
# qemu-img commit -f qcow2 test-sn
qemu-img: First cluster in emptied image is in use
Aborted (core dumped)


Actual results:
Aborted (core dumped) as above.

Expected results:
The snapshot could be committed to its base successfully.


Additional info:

Created attachment 1456629 [details]
gdb_debug_info_all_threads-07052018

This is with a Gluster FUSE mount, interesting.

I can reproduce this with glusterfs 3.8.4-53.el7, but not 4.0.2-1.fc28.  Since this occurs with a fuse mount, it appears the difference is with gluster, and we are getting two different read results.  When I debug via GDB, sometimes it works OK on 3.8.4-53, which makes me think there is a race condition present somewhere.

I'm re-assigning this over to glusterfs, for the reasons given in comment #5.  Since this is reported over a fuse mount, and the bug is not present with later libgfapi versions, this is something that needs to be addressed at the gluster package level.

Prasanna, could you take a look at this?

After evaluating this issue, there are no plans to address it further or fix it in an upcoming release.  Therefore, it is being closed.  If plans change such that this issue will be fixed in an upcoming release, then the bug can be reopened.