consensus/clique: fix race condition (ethereum#24957)

* consensus/clique: remove race condition

* consensus/clique: fix one more signer data race

Co-authored-by: Gary Rong <garyrong0905@gmail.com>

consensus/clique/clique.go

@@ -181,7 +181,7 @@ type Clique struct {
 
  signer common.Address // Ethereum address of the signing key
  signFn SignerFn // Signer function to authorize hashes with
- lock sync.RWMutex // Protects the signer fields
+ lock sync.RWMutex // Protects the signer and proposals fields
 
  // The fields below are for testing only
  fakeDiff bool // Skip difficulty verifications
@@ -509,9 +509,8 @@ func (c *Clique) Prepare(chain consensus.ChainHeaderReader, header *types.Header
  if err != nil {
  return err
  }
+ c.lock.RLock()
  if number%c.config.Epoch != 0 {
- c.lock.RLock()
-
  // Gather all the proposals that make sense voting on
  addresses := make([]common.Address, 0, len(c.proposals))
  for address, authorize := range c.proposals {
@@ -528,10 +527,14 @@ func (c *Clique) Prepare(chain consensus.ChainHeaderReader, header *types.Header
  copy(header.Nonce[:], nonceDropVote)
  }
  }
- c.lock.RUnlock()
  }
+
+ // Copy signer protected by mutex to avoid race condition
+ signer := c.signer
+ c.lock.RUnlock()
+
  // Set the correct difficulty
- header.Difficulty = calcDifficulty(snap, c.signer)
+ header.Difficulty = calcDifficulty(snap, signer)
 
  // Ensure the extra data has all its components
  if len(header.Extra) < extraVanity {
@@ -670,7 +673,10 @@ func (c *Clique) CalcDifficulty(chain consensus.ChainHeaderReader, time uint64,
  if err != nil {
  return nil
  }
- return calcDifficulty(snap, c.signer)
+ c.lock.RLock()
+ signer := c.signer
+ c.lock.RUnlock()
+ return calcDifficulty(snap, signer)
 }
 
 func calcDifficulty(snap *Snapshot, signer common.Address) *big.Int {