txpool slotGauge uint64 underflow (#1907)

txpool/slot_gauge.go

@@ -29,6 +29,25 @@ func (g *slotGauge) increase(slots uint64) {
 	metrics.SetGauge([]string{txPoolMetrics, "slots_used"}, float32(newHeight))
 }
 
+// increaseWithinLimit increases the height of the gauge by the specified slots amount only if the increased height is
+// less than max. Returns true if the height is increased.
+func (g *slotGauge) increaseWithinLimit(slots uint64) (updated bool) {
+	for {
+		old := g.read()
+		newHeight := old + slots
+
+		if newHeight > g.max {
+			return false
+		}
+
+		if atomic.CompareAndSwapUint64(&g.height, old, newHeight) {
+			metrics.SetGauge([]string{txPoolMetrics, "slots_used"}, float32(newHeight))
+
+			return true
+		}
+	}
+}
+
 // decrease decreases the height of the gauge by the specified slots amount.
 func (g *slotGauge) decrease(slots uint64) {
 	newHeight := atomic.AddUint64(&g.height, ^(slots - 1))

txpool/txpool.go

@@ -787,8 +787,6 @@ func (p *TxPool) addTx(origin txOrigin, tx *types.Transaction) error {
 
 	// initialize account for this address once or retrieve existing one
 	account := p.getOrCreateAccount(tx.From)
-	// populate currently free slots
-	slotsFree := p.gauge.freeSlots()
 
 	account.promoted.lock(true)
 	account.enqueued.lock(true)
@@ -827,8 +825,6 @@ func (p *TxPool) addTx(origin txOrigin, tx *types.Transaction) error {
 
 			return ErrReplacementUnderpriced
 		}
-
-		slotsFree += slotsRequired(oldTxWithSameNonce) // add old tx slots
 	} else {
 		if account.enqueued.length() == account.maxEnqueued && tx.Nonce != accountNonce {
 			return ErrMaxEnqueuedLimitReached
@@ -842,27 +838,43 @@ func (p *TxPool) addTx(origin txOrigin, tx *types.Transaction) error {
 		}
 	}
 
-	// check for overflow
-	if slotsRequired(tx) > slotsFree {
-		return ErrTxPoolOverflow
+	slotsAllocated := slotsRequired(tx)
+
+	var slotsFreed uint64
+	if oldTxWithSameNonce != nil {
+		slotsFreed = slotsRequired(oldTxWithSameNonce)
+	}
+
+	var slotsIncreased uint64
+	if slotsAllocated > slotsFreed {
+		slotsIncreased = slotsAllocated - slotsFreed
+		if !p.gauge.increaseWithinLimit(slotsIncreased) {
+			return ErrTxPoolOverflow
+		}
 	}
 
 	// add to index
 	if ok := p.index.add(tx); !ok {
 		metrics.IncrCounter([]string{txPoolMetrics, "already_known_tx"}, 1)
 
+		if slotsIncreased > 0 {
+			p.gauge.decrease(slotsIncreased)
+		}
+
 		return ErrAlreadyKnown
 	}
 
+	if slotsFreed > slotsAllocated {
+		p.gauge.decrease(slotsFreed - slotsAllocated)
+	}
+
 	if oldTxWithSameNonce != nil {
 		p.index.remove(oldTxWithSameNonce)
-		p.gauge.decrease(slotsRequired(oldTxWithSameNonce))
 	} else {
 		metrics.SetGauge([]string{txPoolMetrics, "added_tx"}, 1)
 	}
 
 	account.enqueue(tx, oldTxWithSameNonce != nil) // add or replace tx into account
-	p.gauge.increase(slotsRequired(tx))
 
 	go p.invokePromotion(tx, tx.Nonce <= accountNonce) // don't signal promotion for higher nonce txs