[Bug 15123] getxattr() on cifs sometimes hangs since kernel 5.14

[samba-bugs@samba.org]

https://bugzilla.samba.org/show_bug.cgi?id=15123

--- Comment #1 from Forest <forestix@sonic.net> ---
I can reliably reproduce it booting from this live USB image:
kubuntu-22.04-desktop-amd64.iso

My setup steps when using that live USB environment:

sudo mount.cifs //myserver/dir ~/mnt/dir -o username=myuser,uid=999,gid=999
touch ~/mnt/dir/test{1..5}

Tests and results:
(My reproducer program is called xattrtest in these command lines.)

# 1 thread is fast
# (note the system call duration reported by strace in <> brackets)
$ time ./xattrtest ~/mnt/dir/test{1..5}
real    0m0.079s
user    0m0.003s
sys     0m0.000s
$ strace -Te getxattr ./xattrtest ~/mnt/dir/test1
getxattr("/home/myuser/mnt/dir/test1", "user.baloo.rating", NULL, 0) = -1
ENODATA (No data available) <0.008482>

# 2+ threads are slow
$ time ./xattrtest -t 2 ~/mnt/dir/test{1..5}
real    0m5.118s
user    0m0.005s
sys     0m0.000s
$ strace -Te getxattr ./xattrtest -t 2 ~/mnt/dir/test1
getxattr("/home/myuser/mnt/dir/test1", "user.baloo.rating", NULL, 0) = -1
ENODATA (No data available) <1.018507>

# 2+ threads are fast if I remount with the nouser_xattr option
$ time ./xattrtest -t 2 ~/mnt/dir/test{1..5}
real    0m0.061s
user    0m0.002s
sys     0m0.000s
$ strace -Te getxattr ./xattrtest -t 2 ~/mnt/dir/test1
getxattr("/home/myuser/mnt/dir/test1", "user.baloo.rating", NULL, 0) = -1
EOPNOTSUPP (Operation not supported) <0.000048>

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