fix data race in GetWebAssets (grafana#90939)

Author: diegommm

pkg/api/webassets/webassets.go

@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
+	"sync"
 
 	"github.com/grafana/grafana/pkg/api/dtos"
 	"github.com/grafana/grafana/pkg/services/licensing"
@@ -31,12 +32,21 @@ type EntryPointInfo struct {
 	} `json:"assets,omitempty"`
 }
 
-var entryPointAssetsCache *dtos.EntryPointAssets = nil
+var (
+	entryPointAssetsCacheMu sync.RWMutex           // guard entryPointAssetsCache
+	entryPointAssetsCache   *dtos.EntryPointAssets // TODO: get rid of global state
+)
 
 func GetWebAssets(ctx context.Context, cfg *setting.Cfg, license licensing.Licensing) (*dtos.EntryPointAssets, error) {
-	if cfg.Env != setting.Dev && entryPointAssetsCache != nil {
-		return entryPointAssetsCache, nil
+	entryPointAssetsCacheMu.RLock()
+	ret := entryPointAssetsCache
+	entryPointAssetsCacheMu.RUnlock()
+
+	if cfg.Env != setting.Dev && ret != nil {
+		return ret, nil
 	}
+	entryPointAssetsCacheMu.Lock()
+	defer entryPointAssetsCacheMu.Unlock()
 
 	var err error
 	var result *dtos.EntryPointAssets