autofs: dont trigger mount if it cant succeed

autofs: dont trigger mount if it cant succeed

If a mount namespace contains autofs mounts, and they are propagation
private, and there is no namespace specific automount daemon to handle
possible automounting then attempted path resolution will loop until
MAXSYMLINKS is reached before failing causing quite a bit of noise in
the log.

Add a check for this in autofs ->d_automount() so that the VFS can
immediately return an error in this case. Since the mount is propagation
private an EPERM return seems most appropriate.

Suggested by: Christian Brauner <brauner@kernel.org>

Signed-off-by: Ian Kent <raven@themaw.net>
Link: https://patch.msgid.link/20251118024631.10854-2-raven@themaw.net
Signed-off-by: Christian Brauner <brauner@kernel.org>