Since gfs2_permission may be called either from the VFS (in which case
we need to obtain a shared glock) or from GFS2 (in which case we already
have a glock) we need to test to see whether or not a lock is required.
The original test was buggy due to a potential race. This one should
be safe.

This fixes Red Hat bugzilla #217129
Signed-off-by: NSteven Whitehouse <swhiteho@redhat.com>