ceph: keep reference to parent inode on ceph_dentry

When creating a new dentry we now hold a reference to the parent
inode in the ceph_dentry. This is required due to the new RCU
changes from 949854d0, which set dentry->d_parent to NULL in d_kill before
calling the ->release() callback. If/when that behavior is changed, we can
revert this hack.

Signed-off-by: Yehuda Sadeh <[e-mail]>
Signed-off-by: Sage Weil <[e-mail]>

fs/ceph/dir.c

···
 	}
 	di->dentry = dentry;
 	di->lease_session = NULL;
+	di->parent_inode = igrab(dentry->d_parent->d_inode);
 	dentry->d_fsdata = di;
 	dentry->d_time = jiffies;
 	ceph_dentry_lru_add(dentry);
···
 	u64 snapid = CEPH_NOSNAP;
 
 	if (!IS_ROOT(dentry)) {
-		parent_inode = dentry->d_parent->d_inode;
+		parent_inode = di->parent_inode;
 		if (parent_inode)
 			snapid = ceph_snap(parent_inode);
 	}
···
 		kmem_cache_free(ceph_dentry_cachep, di);
 		dentry->d_fsdata = NULL;
 	}
+	if (parent_inode)
+		iput(parent_inode);
 }
 
 static int ceph_snapdir_d_revalidate(struct dentry *dentry,

fs/ceph/super.h

···
 	struct dentry *dentry;
 	u64 time;
 	u64 offset;
+	struct inode *parent_inode;
 };
 
 struct ceph_inode_xattrs_info {