ceph: allow dentry_lease_is_valid to work under RCU walk

Under rcuwalk, we need to take extra care when dereferencing d_parent.
We want to do that once and pass a pointer to dentry_lease_is_valid.

Also, we must ensure that that function can handle the case where we're
racing with d_release. Check whether "di" is NULL under the d_lock, and
just return 0 if so.

Finally, we still need to kick off a renewal job if the lease is getting
close to expiration. If that's the case, then just drop out of rcuwalk
mode since that could block.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Yan, Zheng <zyan@redhat.com>

fs/ceph/dir.c

@@ -1133,7 +1133,8 @@ void ceph_invalidate_dentry_lease(struct dentry *dentry)
  * Check if dentry lease is valid.  If not, delete the lease.  Try to
  * renew if the least is more than half up.
  */
-static int dentry_lease_is_valid(struct dentry *dentry)
+static int dentry_lease_is_valid(struct dentry *dentry, unsigned int flags,
+				 struct inode *dir)
 {
 	struct ceph_dentry_info *di;
 	struct ceph_mds_session *s;
@@ -1141,12 +1142,11 @@ static int dentry_lease_is_valid(struct dentry *dentry)
 	u32 gen;
 	unsigned long ttl;
 	struct ceph_mds_session *session = NULL;
-	struct inode *dir = NULL;
 	u32 seq = 0;
 
 	spin_lock(&dentry->d_lock);
 	di = ceph_dentry(dentry);
-	if (di->lease_session) {
+	if (di && di->lease_session) {
 		s = di->lease_session;
 		spin_lock(&s->s_gen_ttl_lock);
 		gen = s->s_cap_gen;
@@ -1159,8 +1159,14 @@ static int dentry_lease_is_valid(struct dentry *dentry)
 			valid = 1;
 			if (di->lease_renew_after &&
 			    time_after(jiffies, di->lease_renew_after)) {
-				/* we should renew */
-				dir = d_inode(dentry->d_parent);
+				/*
+				 * We should renew. If we're in RCU walk mode
+				 * though, we can't do that so just return
+				 * -ECHILD.
+				 */
+				if (flags & LOOKUP_RCU) {
+					valid = -ECHILD;
+				} else {
 					session = ceph_get_mds_session(s);
 					seq = di->lease_seq;
 					di->lease_renew_after = 0;
@@ -1168,6 +1174,7 @@ static int dentry_lease_is_valid(struct dentry *dentry)
 				}
 			}
 		}
+	}
 	spin_unlock(&dentry->d_lock);
 
 	if (session) {
@@ -1224,13 +1231,17 @@ static int ceph_d_revalidate(struct dentry *dentry, unsigned int flags)
 	} else if (d_really_is_positive(dentry) &&
 		   ceph_snap(d_inode(dentry)) == CEPH_SNAPDIR) {
 		valid = 1;
-	} else if (dentry_lease_is_valid(dentry) ||
-		   dir_lease_is_valid(dir, dentry)) {
+	} else {
+		valid = dentry_lease_is_valid(dentry, flags, dir);
+		if (valid == -ECHILD)
+			return valid;
+		if (valid || dir_lease_is_valid(dir, dentry)) {
 			if (d_really_is_positive(dentry))
 				valid = ceph_is_any_caps(d_inode(dentry));
 			else
 				valid = 1;
 		}
+	}
 
 	if (!valid) {
 		struct ceph_mds_client *mdsc =