Replace database locks with transactions (#1701)

This commits removes the locks used to guard data integrity for the
database and replaces them with Transactions, turns out that SQL had
a way to deal with this all along.

This reduces the complexity we had with multiple locks that might stack
or recurse (database, nofitifer, mapper). All notifications and state
updates are now triggered _after_ a database change.


Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/policy/acls.go

@@ -905,32 +905,39 @@ func (pol *ACLPolicy) TagsOfNode(
 	validTags := make([]string, 0)
 	invalidTags := make([]string, 0)
 
+	// TODO(kradalby): Why is this sometimes nil? coming from tailNode?
+	if node == nil {
+		return validTags, invalidTags
+	}
+
 	validTagMap := make(map[string]bool)
 	invalidTagMap := make(map[string]bool)
-	for _, tag := range node.Hostinfo.RequestTags {
-		owners, err := expandOwnersFromTag(pol, tag)
-		if errors.Is(err, ErrInvalidTag) {
-			invalidTagMap[tag] = true
+	if node.Hostinfo != nil {
+		for _, tag := range node.Hostinfo.RequestTags {
+			owners, err := expandOwnersFromTag(pol, tag)
+			if errors.Is(err, ErrInvalidTag) {
+				invalidTagMap[tag] = true
 
-			continue
-		}
-		var found bool
-		for _, owner := range owners {
-			if node.User.Name == owner {
-				found = true
+				continue
+			}
+			var found bool
+			for _, owner := range owners {
+				if node.User.Name == owner {
+					found = true
+				}
+			}
+			if found {
+				validTagMap[tag] = true
+			} else {
+				invalidTagMap[tag] = true
 			}
 		}
-		if found {
-			validTagMap[tag] = true
-		} else {
-			invalidTagMap[tag] = true
+		for tag := range invalidTagMap {
+			invalidTags = append(invalidTags, tag)
+		}
+		for tag := range validTagMap {
+			validTags = append(validTags, tag)
 		}
-	}
-	for tag := range invalidTagMap {
-		invalidTags = append(invalidTags, tag)
-	}
-	for tag := range validTagMap {
-		validTags = append(validTags, tag)
 	}
 
 	return validTags, invalidTags