eth: quick canceling block inserting when debug_setHead is invoked (#32067)

If Geth is engaged in a long-run block synchronization, such as a full
syncing over a large number of blocks, invoking `debug_setHead` will
cause `downloader.Cancel` to wait for all fetchers to stop first.
This can be time-consuming, particularly for the block processing
thread.

To address this, we manually call `blockchain.StopInsert` to interrupt
the blocking processing thread and allow it to exit immediately, and
after that call `blockchain.ResumeInsert` to resume the block
downloading process.

Additionally, we add a sanity check for the input block number of
`debug_setHead` to ensure its validity.

---------

Signed-off-by: jsvisa <delweng@gmail.com>
Co-authored-by: Gary Rong <garyrong0905@gmail.com>

core/blockchain.go

@@ -1244,7 +1244,7 @@ func (bc *BlockChain) stopWithoutSaving() {
 	bc.scope.Close()
 
 	// Signal shutdown to all goroutines.
-	bc.StopInsert()
+	bc.InterruptInsert(true)
 
 	// Now wait for all chain modifications to end and persistent goroutines to exit.
 	//
@@ -1318,11 +1318,15 @@ func (bc *BlockChain) Stop() {
 	log.Info("Blockchain stopped")
 }
 
-// StopInsert interrupts all insertion methods, causing them to return
+// InterruptInsert interrupts all insertion methods, causing them to return
-// errInsertionInterrupted as soon as possible. Insertion is permanently disabled after
+// errInsertionInterrupted as soon as possible, or resume the chain insertion
-// calling this method.
+// if required.
-func (bc *BlockChain) StopInsert() {
+func (bc *BlockChain) InterruptInsert(on bool) {
-	bc.procInterrupt.Store(true)
+	if on {
+		bc.procInterrupt.Store(true)
+	} else {
+		bc.procInterrupt.Store(false)
+	}
 }
 
 // insertStopped returns true after StopInsert has been called.

eth/downloader/downloader.go

@@ -199,8 +199,8 @@ type BlockChain interface {
 	// InsertChain inserts a batch of blocks into the local chain.
 	InsertChain(types.Blocks) (int, error)
 
-	// StopInsert interrupts the inserting process.
+	// InterruptInsert whether disables the chain insertion.
-	StopInsert()
+	InterruptInsert(on bool)
 
 	// InsertReceiptChain inserts a batch of blocks along with their receipts
 	// into the local chain. Blocks older than the specified `ancientLimit`
@@ -630,16 +630,15 @@ func (d *Downloader) cancel() {
 // Cancel aborts all of the operations and waits for all download goroutines to
 // finish before returning.
 func (d *Downloader) Cancel() {
+	d.blockchain.InterruptInsert(true)
 	d.cancel()
 	d.cancelWg.Wait()
+	d.blockchain.InterruptInsert(false)
 }
 
 // Terminate interrupts the downloader, canceling all pending operations.
 // The downloader cannot be reused after calling Terminate.
 func (d *Downloader) Terminate() {
-	// Signal to stop inserting in-flight blocks
-	d.blockchain.StopInsert()
-
 	// Close the termination channel (make sure double close is allowed)
 	d.quitLock.Lock()
 	select {

internal/ethapi/api.go

@@ -1831,8 +1831,16 @@ func (api *DebugAPI) ChaindbCompact() error {
 }
 
 // SetHead rewinds the head of the blockchain to a previous block.
-func (api *DebugAPI) SetHead(number hexutil.Uint64) {
+func (api *DebugAPI) SetHead(number hexutil.Uint64) error {
+	header := api.b.CurrentHeader()
+	if header == nil {
+		return errors.New("current header is not available")
+	}
+	if header.Number.Uint64() <= uint64(number) {
+		return errors.New("not allowed to rewind to a future block")
+	}
 	api.b.SetHead(uint64(number))
+	return nil
 }
 
 // NetAPI offers network related RPC methods