Revert parts of 938cfeb

When read and writing the UID/GID, we always want the value
relative to the root user namespace, the kernel will take care
of remapping this to the user namespace for us.

Calling from_kuid(user_ns, uid) with a unmapped uid will return -1
as that uid is outside of the scope of that namespace, and will result
in the files inside the namespace all being owned by 'nobody' and not
being allowed to call chmod or chown on them.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Allan Jude <allan@klarasystems.com>
Closes openzfs#12263

include/os/linux/kernel/linux/vfs_compat.h

@@ -296,11 +296,7 @@ static inline struct dentry *file_dentry(const struct file *f)
 
 static inline uid_t zfs_uid_read_impl(struct inode *ip)
 {
-#ifdef HAVE_SUPER_USER_NS
-	return (from_kuid(ip->i_sb->s_user_ns, ip->i_uid));
-#else
 	return (from_kuid(kcred->user_ns, ip->i_uid));
-#endif
 }
 
 static inline uid_t zfs_uid_read(struct inode *ip)
@@ -310,11 +306,7 @@ static inline uid_t zfs_uid_read(struct inode *ip)
 
 static inline gid_t zfs_gid_read_impl(struct inode *ip)
 {
-#ifdef HAVE_SUPER_USER_NS
-	return (from_kgid(ip->i_sb->s_user_ns, ip->i_gid));
-#else
 	return (from_kgid(kcred->user_ns, ip->i_gid));
-#endif
 }
 
 static inline gid_t zfs_gid_read(struct inode *ip)
@@ -324,20 +316,12 @@ static inline gid_t zfs_gid_read(struct inode *ip)
 
 static inline void zfs_uid_write(struct inode *ip, uid_t uid)
 {
-#ifdef HAVE_SUPER_USER_NS
-	ip->i_uid = make_kuid(ip->i_sb->s_user_ns, uid);
-#else
 	ip->i_uid = make_kuid(kcred->user_ns, uid);
-#endif
 }
 
 static inline void zfs_gid_write(struct inode *ip, gid_t gid)
 {
-#ifdef HAVE_SUPER_USER_NS
-	ip->i_gid = make_kgid(ip->i_sb->s_user_ns, gid);
-#else
 	ip->i_gid = make_kgid(kcred->user_ns, gid);
-#endif
 }
 
 /*