ceph: fix cache revoke race

handle following sequence of events:

- non-auth MDS revokes Fc cap. queue invalidate work
- auth MDS issues Fc cap through request reply. i_rdcache_gen gets
  increased.
- invalidate work runs. it finds i_rdcache_revoking != i_rdcache_gen,
  so it does nothing.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index 7fa78a7..891cda8 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -528,6 +528,8 @@
 }
 extern int __ceph_mark_dirty_caps(struct ceph_inode_info *ci, int mask);
 
+extern int __ceph_caps_revoking_other(struct ceph_inode_info *ci,
+				      struct ceph_cap *ocap, int mask);
 extern int ceph_caps_revoking(struct ceph_inode_info *ci, int mask);
 extern int __ceph_caps_used(struct ceph_inode_info *ci);