Sorry for the necro but I’m having the exact same issue.
#grep "rbd1 rw" /proc/*/mountinfo 2>/dev/null
/proc/3517630/mountinfo:360 348 252:16 / /var/snap/lxd/common/lxd/storage-pools/remote/containers/among-us rw,relatime shared:76 - ext4 /dev/rbd1 rw,discard,stripe=16
/proc/3517655/mountinfo:360 348 252:16 / /var/snap/lxd/common/lxd/storage-pools/remote/containers/among-us rw,relatime shared:76 - ext4 /dev/rbd1 rw,discard,stripe=16
/proc/3517692/mountinfo:360 348 252:16 / /var/snap/lxd/common/lxd/storage-pools/remote/containers/among-us rw,relatime shared:76 - ext4 /dev/rbd1 rw,discard,stripe=16
/proc/3537155/mountinfo:360 348 252:16 / /var/snap/lxd/common/lxd/storage-pools/remote/containers/among-us rw,relatime shared:76 - ext4 /dev/rbd1 rw,discard,stripe=16
/proc/3537175/mountinfo:360 348 252:16 / /var/snap/lxd/common/lxd/storage-pools/remote/containers/among-us rw,relatime shared:76 - ext4 /dev/rbd1 rw,discard,stripe=16
/proc/3554782/mountinfo:360 348 252:16 / /var/snap/lxd/common/lxd/storage-pools/remote/containers/among-us rw,relatime shared:76 - ext4 /dev/rbd1 rw,discard,stripe=16
/proc/3555055/mountinfo:360 348 252:16 / /var/snap/lxd/common/lxd/storage-pools/remote/containers/among-us rw,relatime shared:76 - ext4 /dev/rbd1 rw,discard,stripe=16
/proc/3555152/mountinfo:360 348 252:16 / /var/snap/lxd/common/lxd/storage-pools/remote/containers/among-us rw,relatime shared:76 - ext4 /dev/rbd1 rw,discard,stripe=16
/proc/3555169/mountinfo:360 348 252:16 / /var/snap/lxd/common/lxd/storage-pools/remote/containers/among-us rw,relatime shared:76 - ext4 /dev/rbd1 rw,discard,stripe=16
/proc/3556119/mountinfo:360 348 252:16 / /var/snap/lxd/common/lxd/storage-pools/remote/containers/among-us rw,relatime shared:76 - ext4 /dev/rbd1 rw,discard,stripe=16
/proc/3556346/mountinfo:360 348 252:16 / /var/snap/lxd/common/lxd/storage-pools/remote/containers/among-us rw,relatime shared:76 - ext4 /dev/rbd1 rw,discard,stripe=16
/proc/3556408/mountinfo:360 348 252:16 / /var/snap/lxd/common/lxd/storage-pools/remote/containers/among-us rw,relatime shared:76 - ext4 /dev/rbd1 rw,discard,stripe=16
/proc/3556722/mountinfo:360 348 252:16 / /var/snap/lxd/common/lxd/storage-pools/remote/containers/among-us rw,relatime shared:76 - ext4 /dev/rbd1 rw,discard,stripe=16
/proc/3556809/mountinfo:360 348 252:16 / /var/snap/lxd/common/lxd/storage-pools/remote/containers/among-us rw,relatime shared:76 - ext4 /dev/rbd1 rw,discard,stripe=16
/proc/3556919/mountinfo:360 348 252:16 / /var/snap/lxd/common/lxd/storage-pools/remote/containers/among-us rw,relatime shared:76 - ext4 /dev/rbd1 rw,discard,stripe=16
/proc/3556973/mountinfo:360 348 252:16 / /var/snap/lxd/common/lxd/storage-pools/remote/containers/among-us rw,relatime shared:76 - ext4 /dev/rbd1 rw,discard,stripe=16
Sadly for me the nsenter command does not appear to be doing anything.
# nsenter -t 3517630 -m - umount /var/snap/lxd/common/lxd/storage-pools/remote/containers/among-us
nsenter: failed to execute -: No such file or directory
Any other way to solve this?