[REGRESSION] in Linux 7.0: empty CIFS mount point with vers=1.0

[Kris Karas (Bug Reporting)]

A bit late to the party, sorry, I should have reported this in 7.0-rcX.

When mounting a CIFS share with vers=1.0, the mount "succeeds" (is added 
to /proc/mounts) but the mountpoint is completely empty.  Even "." and 
".." are missing.  Blindly accessing a known file results in "no such 
file or directory".

Kernels 6.19 and below are not affected.  Using vers=2.0 or vers=3.1.1 
(etc) works fine, but "UNIX File Extensions" is still necessary for my 
workload.  (While "posix" extensions in vers=3.1.1 against Samba Stable 
is getting better, it's not there yet, details on request.)

Example:
    # ls -al /mnt/tmp
    Total 8
    drwxr-xr-x  2 root root 4096 Sep 25  2006 ./
    drwxr-xr-x 12 root root 4096 Apr 11 03:32 ../
    ----------  1 root root    0 Dec 22  2018 filesystem.not.mounted
    # mount -t cifs -o vers=1.0,cred=.creds //Server/Share /mnt/tmp
    # ls -al /mnt/tmp
    Total 0
    #

If Greg KH were reading this, I just know he'd say,
"can you bisect?"  :-)  OK, the winner of the bisect is:

> 4fc3a433c13944ee5766ec5b9bf6f1eb4d29b880 is the first bad commit
> commit 4fc3a433c13944ee5766ec5b9bf6f1eb4d29b880
> Author: Paulo Alcantara <pc@xxxxxxxxxxxxx>
> Date:   Mon Feb 23 13:34:35 2026 -0300
>
>     smb: client: use atomic_t for mnt_cifs_flags
>     
>     Use atomic_t for cifs_sb_info::mnt_cifs_flags as it's currently
>     accessed locklessly and may be changed concurrently in mount/remount
>     and reconnect paths.

I added Paulo to the CC's.

Kris