ceph: add ceph_change_snap_realm() helper

Consolidate some fiddly code for changing an inode's snap_realm
into a new helper function, and change the callers to use it.

While we're in here, nothing uses the i_snap_realm_counter field, so
remove that from the inode.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Luis Henriques <lhenriques@suse.de>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/caps.c

@@ -704,23 +704,7 @@ void ceph_add_cap(struct inode *inode,
 		struct ceph_snap_realm *realm = ceph_lookup_snap_realm(mdsc,
 							       realmino);
 		if (realm) {
-			struct ceph_snap_realm *oldrealm = ci->i_snap_realm;
-			if (oldrealm) {
-				spin_lock(&oldrealm->inodes_with_caps_lock);
-				list_del_init(&ci->i_snap_realm_item);
-				spin_unlock(&oldrealm->inodes_with_caps_lock);
-			}
-
-			spin_lock(&realm->inodes_with_caps_lock);
-			list_add(&ci->i_snap_realm_item,
-				 &realm->inodes_with_caps);
-			ci->i_snap_realm = realm;
-			if (realm->ino == ci->i_vino.ino)
-				realm->inode = inode;
-			spin_unlock(&realm->inodes_with_caps_lock);
-
-			if (oldrealm)
-				ceph_put_snap_realm(mdsc, oldrealm);
+			ceph_change_snap_realm(inode, realm);
 		} else {
 			pr_err("ceph_add_cap: couldn't find snap realm %llx\n",
 			       realmino);
@@ -1112,20 +1096,6 @@ int ceph_is_any_caps(struct inode *inode)
 	return ret;
 }
 
-static void drop_inode_snap_realm(struct ceph_inode_info *ci)
-{
-	struct ceph_snap_realm *realm = ci->i_snap_realm;
-	spin_lock(&realm->inodes_with_caps_lock);
-	list_del_init(&ci->i_snap_realm_item);
-	ci->i_snap_realm_counter++;
-	ci->i_snap_realm = NULL;
-	if (realm->ino == ci->i_vino.ino)
-		realm->inode = NULL;
-	spin_unlock(&realm->inodes_with_caps_lock);
-	ceph_put_snap_realm(ceph_sb_to_client(ci->vfs_inode.i_sb)->mdsc,
-			    realm);
-}
-
 /*
  * Remove a cap.  Take steps to deal with a racing iterate_session_caps.
  *
@@ -1201,7 +1171,7 @@ void __ceph_remove_cap(struct ceph_cap *cap, bool queue_release)
 		 * keep i_snap_realm.
 		 */
 		if (ci->i_wr_ref == 0 && ci->i_snap_realm)
-			drop_inode_snap_realm(ci);
+			ceph_change_snap_realm(&ci->vfs_inode, NULL);
 
 		__cap_delay_cancel(mdsc, ci);
 	}
@@ -3084,7 +3054,7 @@ static void __ceph_put_cap_refs(struct ceph_inode_info *ci, int had,
 			}
 			/* see comment in __ceph_remove_cap() */
 			if (!__ceph_is_any_real_caps(ci) && ci->i_snap_realm)
-				drop_inode_snap_realm(ci);
+				ceph_change_snap_realm(inode, NULL);
 		}
 	}
 	if (check_flushsnaps && __ceph_have_pending_cap_snap(ci)) {

fs/ceph/inode.c

@@ -581,16 +581,9 @@ void ceph_evict_inode(struct inode *inode)
 	 */
 	if (ci->i_snap_realm) {
 		if (ceph_snap(inode) == CEPH_NOSNAP) {
-			struct ceph_snap_realm *realm = ci->i_snap_realm;
 			dout(" dropping residual ref to snap realm %p\n",
-			     realm);
-			spin_lock(&realm->inodes_with_caps_lock);
-			list_del_init(&ci->i_snap_realm_item);
-			ci->i_snap_realm = NULL;
-			if (realm->ino == ci->i_vino.ino)
-				realm->inode = NULL;
-			spin_unlock(&realm->inodes_with_caps_lock);
-			ceph_put_snap_realm(mdsc, realm);
+			     ci->i_snap_realm);
+			ceph_change_snap_realm(inode, NULL);
 		} else {
 			ceph_put_snapid_map(mdsc, ci->i_snapid_map);
 			ci->i_snap_realm = NULL;

fs/ceph/snap.c

@@ -849,6 +849,43 @@ static void flush_snaps(struct ceph_mds_client *mdsc)
 	dout("flush_snaps done\n");
 }
 
+/**
+ * ceph_change_snap_realm - change the snap_realm for an inode
+ * @inode: inode to move to new snap realm
+ * @realm: new realm to move inode into (may be NULL)
+ *
+ * Detach an inode from its old snaprealm (if any) and attach it to
+ * the new snaprealm (if any). The old snap realm reference held by
+ * the inode is put. If realm is non-NULL, then the caller's reference
+ * to it is taken over by the inode.
+ */
+void ceph_change_snap_realm(struct inode *inode, struct ceph_snap_realm *realm)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	struct ceph_mds_client *mdsc = ceph_inode_to_client(inode)->mdsc;
+	struct ceph_snap_realm *oldrealm = ci->i_snap_realm;
+
+	lockdep_assert_held(&ci->i_ceph_lock);
+
+	if (oldrealm) {
+		spin_lock(&oldrealm->inodes_with_caps_lock);
+		list_del_init(&ci->i_snap_realm_item);
+		if (oldrealm->ino == ci->i_vino.ino)
+			oldrealm->inode = NULL;
+		spin_unlock(&oldrealm->inodes_with_caps_lock);
+		ceph_put_snap_realm(mdsc, oldrealm);
+	}
+
+	ci->i_snap_realm = realm;
+
+	if (realm) {
+		spin_lock(&realm->inodes_with_caps_lock);
+		list_add(&ci->i_snap_realm_item, &realm->inodes_with_caps);
+		if (realm->ino == ci->i_vino.ino)
+			realm->inode = inode;
+		spin_unlock(&realm->inodes_with_caps_lock);
+	}
+}
 
 /*
  * Handle a snap notification from the MDS.
@@ -935,7 +972,6 @@ void ceph_handle_snap(struct ceph_mds_client *mdsc,
 			};
 			struct inode *inode = ceph_find_inode(sb, vino);
 			struct ceph_inode_info *ci;
-			struct ceph_snap_realm *oldrealm;
 
 			if (!inode)
 				continue;
@@ -960,27 +996,10 @@ void ceph_handle_snap(struct ceph_mds_client *mdsc,
 			}
 			dout(" will move %p to split realm %llx %p\n",
 			     inode, realm->ino, realm);
-			/*
-			 * Move the inode to the new realm
-			 */
-			oldrealm = ci->i_snap_realm;
-			spin_lock(&oldrealm->inodes_with_caps_lock);
-			list_del_init(&ci->i_snap_realm_item);
-			spin_unlock(&oldrealm->inodes_with_caps_lock);
-
-			spin_lock(&realm->inodes_with_caps_lock);
-			list_add(&ci->i_snap_realm_item,
-				 &realm->inodes_with_caps);
-			ci->i_snap_realm = realm;
-			if (realm->ino == ci->i_vino.ino)
-                                realm->inode = inode;
-			spin_unlock(&realm->inodes_with_caps_lock);
-
-			spin_unlock(&ci->i_ceph_lock);
 
 			ceph_get_snap_realm(mdsc, realm);
-			ceph_put_snap_realm(mdsc, oldrealm);
-
+			ceph_change_snap_realm(inode, realm);
+			spin_unlock(&ci->i_ceph_lock);
 			iput(inode);
 			continue;
 

fs/ceph/super.h

@@ -418,7 +418,6 @@ struct ceph_inode_info {
 		struct ceph_snap_realm *i_snap_realm; /* snap realm (if caps) */
 		struct ceph_snapid_map *i_snapid_map; /* snapid -> dev_t */
 	};
-	int i_snap_realm_counter; /* snap realm (if caps) */
 	struct list_head i_snap_realm_item;
 	struct list_head i_snap_flush_item;
 	struct timespec64 i_btime;
@@ -929,6 +928,7 @@ extern void ceph_put_snap_realm(struct ceph_mds_client *mdsc,
 extern int ceph_update_snap_trace(struct ceph_mds_client *m,
 				  void *p, void *e, bool deletion,
 				  struct ceph_snap_realm **realm_ret);
+void ceph_change_snap_realm(struct inode *inode, struct ceph_snap_realm *realm);
 extern void ceph_handle_snap(struct ceph_mds_client *mdsc,
 			     struct ceph_mds_session *session,
 			     struct ceph_msg *msg);