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+++ This bug was initially created as a clone of Bug #2151869 +++

--- Additional comment from Michal Privoznik on 2022-12-20 11:24:28 CET ---

Indeed. There's something terribly broken (in kernel perhaps?):

kernel-5.14.0-212.el9.x86_64
systemd-252-2.el9.x86_64

1) just to make sure mount events are being propagated:

# mount --make-rshared /

2) check hugetlbfs mounts:

# mount | grep huge
hugetlbfs on /dev/hugepages type hugetlbfs (rw,relatime,seclabel,pagesize=2M)

3) in another terminal, unshare mount namespace:

# unshare -m

4) verify that the hugetlbfs is mounted (from inside the NS):

# mount | grep huge
hugetlbfs on /dev/hugepages type hugetlbfs (rw,relatime,seclabel,pagesize=2M)

5) now, mount another hugetlbfs (from the parent NS, NOT the one just unshared):

# mount -t hugetlbfs -o pagesize=1G hugetlbfs /dev/hugepages1G

6) verify the mount got propagated (from the NS):

# mount | grep huge
hugetlbfs on /dev/hugepages type hugetlbfs (rw,relatime,seclabel,pagesize=2M)


Therefore, this is completely independent of libvirt and should be reported against kernel for further investigation. Then, we can revisit our bug.

Setting TestBlocker keyword since this is blocking verification of the original bug.

(In reply to Michal Privoznik from comment #0)
> 1) just to make sure mount events are being propagated:
> 
> # mount --make-rshared /
> 
> 2) check hugetlbfs mounts:
> 
> # mount | grep huge
> hugetlbfs on /dev/hugepages type hugetlbfs (rw,relatime,seclabel,pagesize=2M)
> 
> 3) in another terminal, unshare mount namespace:
> 
> # unshare -m

Let's stop at this step.

From unshare(1) manpage:
```
unshare since util-linux version 2.27 automatically sets propagation to private in a new mount namespace to make sure that the new namespace is really unshared. It’s possible to disable this feature with option --propagation unchanged. Note that private is the kernel default.
```

If I run the command with the option, all subsequent steps work as you would expect:

# unshare --mount --propagation unchanged

> Therefore, this is completely independent of libvirt and should be reported
> against kernel for further investigation. Then, we can revisit our bug.

I don't know anything about the original bug, but the steps from the description is fully consistent with the behavior described in the documentation.