core/rawdb, eth/downloader: align 64bit atomic fields

core/rawdb/freezer.go

@@ -66,8 +66,12 @@ const (
 //   reserving it for go-ethereum. This would also reduce the memory requirements
 //   of Geth, and thus also GC overhead.
 type freezer struct {
-	tables       map[string]*freezerTable // Data tables for storing everything
+	// WARNING: The `frozen` field is accessed atomically. On 32 bit platforms, only
+	// 64-bit aligned fields can be atomic. The struct is guaranteed to be so aligned,
+	// so take advantage of that (https://golang.org/pkg/sync/atomic/#pkg-note-BUG).
 	frozen uint64 // Number of blocks already frozen
+
+	tables       map[string]*freezerTable // Data tables for storing everything
 	instanceLock fileutil.Releaser        // File-system lock to prevent double opens
 }
 

core/rawdb/freezer_table.go

@@ -73,6 +73,11 @@ func (i *indexEntry) marshallBinary() []byte {
 // It consists of a data file (snappy encoded arbitrary data blobs) and an indexEntry
 // file (uncompressed 64 bit indices into the data file).
 type freezerTable struct {
+	// WARNING: The `items` field is accessed atomically. On 32 bit platforms, only
+	// 64-bit aligned fields can be atomic. The struct is guaranteed to be so aligned,
+	// so take advantage of that (https://golang.org/pkg/sync/atomic/#pkg-note-BUG).
+	items uint64 // Number of items stored in the table (including items removed from tail)
+
 	noCompression bool   // if true, disables snappy compression. Note: does not work retroactively
 	maxFileSize   uint32 // Max file size for data-files
 	name          string
@@ -86,7 +91,6 @@ type freezerTable struct {
 
 	// In the case that old items are deleted (from the tail), we use itemOffset
 	// to count how many historic items have gone missing.
-	items      uint64 // Number of items stored in the table (including items removed from tail)
 	itemOffset uint32 // Offset (number of discarded items)
 
 	headBytes  uint32        // Number of bytes written to the head file

eth/downloader/downloader.go

@@ -98,6 +98,13 @@ var (
 )
 
 type Downloader struct {
+	// WARNING: The `rttEstimate` and `rttConfidence` fields are accessed atomically.
+	// On 32 bit platforms, only 64-bit aligned fields can be atomic. The struct is
+	// guaranteed to be so aligned, so take advantage of that. For more information,
+	// see https://golang.org/pkg/sync/atomic/#pkg-note-BUG.
+	rttEstimate   uint64 // Round trip time to target for download requests
+	rttConfidence uint64 // Confidence in the estimated RTT (unit: millionths to allow atomic ops)
+
 	mode SyncMode       // Synchronisation mode defining the strategy used (per sync cycle)
 	mux  *event.TypeMux // Event multiplexer to announce sync operation events
 
@@ -109,9 +116,6 @@ type Downloader struct {
 	stateDB    ethdb.Database  // Database to state sync into (and deduplicate via)
 	stateBloom *trie.SyncBloom // Bloom filter for fast trie node existence checks
 
-	rttEstimate   uint64 // Round trip time to target for download requests
-	rttConfidence uint64 // Confidence in the estimated RTT (unit: millionths to allow atomic ops)
-
 	// Statistics
 	syncStatsChainOrigin uint64 // Origin block number where syncing started at
 	syncStatsChainHeight uint64 // Highest block number known when syncing started