IAM: Block while loading users (#11671)

While starting up a request that needs all IAM data will start another load operation if the first on startup hasn't finished. This slows down both operations.

Block these requests until initial load has completed.

Blocking calls will be ListPolicies, ListUsers, ListServiceAccounts, ListGroups - and the calls that eventually trigger these. These will wait for the initial load to complete.

Fixes issue seen in #11305

cmd/iam.go

@@ -220,8 +220,10 @@ type IAMSys struct {
 	iamGroupPolicyMap map[string]MappedPolicy
 
 	// Persistence layer for IAM subsystem
-	store         IAMStorageAPI
-	storeFallback bool
+	store IAMStorageAPI
+
+	// configLoaded will be closed and remain so after first load.
+	configLoaded chan struct{}
 }
 
 // IAMUserType represents a user type inside MinIO server
@@ -554,7 +556,11 @@ func (sys *IAMSys) Load(ctx context.Context, store IAMStorageAPI) error {
 	}
 
 	sys.buildUserGroupMemberships()
-	sys.storeFallback = false
+	select {
+	case <-sys.configLoaded:
+	default:
+		close(sys.configLoaded)
+	}
 	return nil
 }
 
@@ -732,15 +738,7 @@ func (sys *IAMSys) ListPolicies() (map[string]iampolicy.Policy, error) {
 		return nil, errServerNotInitialized
 	}
 
-	sys.store.rlock()
-	fallback := sys.storeFallback
-	sys.store.runlock()
-
-	if fallback {
-		if err := sys.store.loadAll(context.Background(), sys); err != nil {
-			return nil, err
-		}
-	}
+	<-sys.configLoaded
 
 	sys.store.rlock()
 	defer sys.store.runlock()
@@ -915,15 +913,7 @@ func (sys *IAMSys) ListUsers() (map[string]madmin.UserInfo, error) {
 		return nil, errIAMActionNotAllowed
 	}
 
-	sys.store.rlock()
-	fallback := sys.storeFallback
-	sys.store.runlock()
-
-	if fallback {
-		if err := sys.store.loadAll(context.Background(), sys); err != nil {
-			return nil, err
-		}
-	}
+	<-sys.configLoaded
 
 	sys.store.rlock()
 	defer sys.store.runlock()
@@ -995,10 +985,9 @@ func (sys *IAMSys) GetUserInfo(name string) (u madmin.UserInfo, err error) {
 		return u, errServerNotInitialized
 	}
 
-	sys.store.rlock()
-	fallback := sys.storeFallback
-	sys.store.runlock()
-	if fallback {
+	select {
+	case <-sys.configLoaded:
+	default:
 		sys.loadUserFromStore(name)
 	}
 
@@ -1178,15 +1167,7 @@ func (sys *IAMSys) ListServiceAccounts(ctx context.Context, accessKey string) ([
 		return nil, errServerNotInitialized
 	}
 
-	sys.store.rlock()
-	fallback := sys.storeFallback
-	sys.store.runlock()
-
-	if fallback {
-		if err := sys.store.loadAll(context.Background(), sys); err != nil {
-			return nil, err
-		}
-	}
+	<-sys.configLoaded
 
 	sys.store.rlock()
 	defer sys.store.runlock()
@@ -1355,11 +1336,12 @@ func (sys *IAMSys) GetUser(accessKey string) (cred auth.Credentials, ok bool) {
 		return cred, false
 	}
 
-	sys.store.rlock()
-	fallback := sys.storeFallback
-	sys.store.runlock()
-	if fallback {
+	fallback := false
+	select {
+	case <-sys.configLoaded:
+	default:
 		sys.loadUserFromStore(accessKey)
+		fallback = true
 	}
 
 	sys.store.rlock()
@@ -1619,15 +1601,7 @@ func (sys *IAMSys) ListGroups() (r []string, err error) {
 		return nil, errIAMActionNotAllowed
 	}
 
-	sys.store.rlock()
-	fallback := sys.storeFallback
-	sys.store.runlock()
-
-	if fallback {
-		if err := sys.store.loadAll(context.Background(), sys); err != nil {
-			return nil, err
-		}
-	}
+	<-sys.configLoaded
 
 	sys.store.rlock()
 	defer sys.store.runlock()
@@ -2182,6 +2156,6 @@ func NewIAMSys() *IAMSys {
 		iamGroupPolicyMap:       make(map[string]MappedPolicy),
 		iamGroupsMap:            make(map[string]GroupInfo),
 		iamUserGroupMemberships: make(map[string]set.StringSet),
-		storeFallback:           true,
+		configLoaded:            make(chan struct{}),
 	}
 }