Cifs mounts get unmounted sporadically

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Environment

SUSE Linux Enterprise Server 15
SUSE Linux Enterprise Server 12

Situation

Multiple cifs mounts get unmounted sporadically.
Cifs mounts can be mounted manually after they are unmounted and get remounted successfully during reboot.
Running df -h hangs or takes a long time to come back if at all. Ctrl-C of the df -h command and running a
grep -i cifs /proc/mounts | wc -l
show that the count of the cifs mounts is lower than what should be mounted.

Resolution

The SLES12 SP3 kernel maintenance update, kernel-default-4.4.180-94.138.1 released in February 2021 includes the patch to resolve the problem. Updates for other SLES/SP versions will follow.

Cause

The kernel is doing some checks on each path elements when doing df.
For the nested mount the VFS layer is put()-ing the dentry of the nested point which triggers the umount().

Disclaimer

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