core, eth: abort snapshot generation on snap sync and resume later

core/blockchain.go

@@ -640,7 +640,8 @@ func (bc *BlockChain) FastSyncCommitHead(hash common.Hash) error {
 	headBlockGauge.Update(int64(block.NumberU64()))
 	bc.chainmu.Unlock()
 
-	// Destroy any existing state snapshot and regenerate it in the background
+	// Destroy any existing state snapshot and regenerate it in the background,
+	// also resuming the normal maintenance of any previously paused snapshot.
 	if bc.snaps != nil {
 		bc.snaps.Rebuild(block.Root())
 	}