Go Concurrency Safety

Injectable Skill: Go Concurrency Safety

L1 trigger: L1_PATTERN=true AND target language = Go Inject Into: Every L1 depth agent working on Go code, in addition to the main skill Finding prefix: [GO-N] Status: v0.1 draft, Round 4 exemplars pending

When This Skill Activates

Supplement to the main L1 skills when the target is written in Go. It codifies the Go-specific traps that turn otherwise-correct logic into production bugs. These are drawn from the Cosmos-SDK, Geth, Erigon, and CometBFT bug histories.

1. Map Iteration Non-Determinism

Go maps iterate in unspecified order. Production bug class: any consensus computation that ranges over a map[K]V and uses the order in its output will produce different results on different nodes.

Detection:

• Ast-grep for $_, $_ := range $MAP where $MAP is declared as map[...]...
• For each hit in a consensus-critical path, check if the iteration result affects any stored state, signed message, or hash input

Fix pattern:

keys := make([]string, 0, len(m))
for k := range m {
    keys = append(keys, k)
}
sort.Strings(keys)
for _, k := range keys {
    v := m[k]
    // use (k, v)
}

Alternative: use btree or sort.SliceStable on a converted slice.

Tag: [GO-MAP-ITER:{loc}:{consumer}]

2. Goroutine Leaks

Goroutines that are started but never terminated. Over hours/days, a leak accumulates and eventually OOMs the node.

Common patterns:

• Goroutine blocked on <-ch where the sender path can return without sending
• Goroutine blocked on http.Get / network call without context timeout
• Goroutine in a for loop without a cancellation check
• Goroutine spawned inside a handler that outlives the handler's parent context

Detection:

• Ast-grep go $FUNC(...) / go func() { ... }()
• For each, trace the function body: is there a termination condition? Is it guaranteed to fire?
• Check every select inside: does it have a case <-ctx.Done()?

Tag: [GO-GOROUTINE-LEAK:{spawn-loc}:{blocked-on}]

3. Mutex Deadlock Risk

Locking order inversions cause deadlocks. In node clients, locks are often acquired across subsystem boundaries (consensus holds lock A, calls into p2p which acquires lock B; p2p holds lock B, calls into consensus which acquires lock A → deadlock).

Detection:

• For every function that acquires 2+ mutexes (directly or via called functions), determine the lock order
• Look for lock order inversions across the same two locks
• Look for Lock / Unlock pairs with an early return that skips Unlock (prefer defer Unlock)

Tag: [GO-LOCK-ORDER:{lock-a}:{lock-b}:{inversion-site}]

4. Channel Send on Closed Channel

Sending on a closed channel panics. In Go, closing a channel you don't own is usually wrong.

Detection:

• Every close(ch): who owns ch? Can another goroutine send on it after close?
• for _, x := range ch pattern: correct consumer side; check producer side always closes exactly once

Tag: [GO-CLOSED-CHAN:{loc}]

5. Panic Boundaries

A goroutine panic crashes the whole process (unless recovered). In RPC handlers, HTTP middleware typically recovers; in background workers, often not.

Detection:

• For each go func() in background code: is the first line defer func() { recover() }?
• For each handler that calls user input-parsing code: is there a recover boundary?
• panic() in consensus code: should never happen; any panic inside the consensus package is a bug

Tag: [GO-PANIC:{loc}:{recovered}]

6. Context Cancellation Propagation

The context.Context pattern propagates cancellation. Every long-running operation should accept a context and check it.

Detection:

• Every function in a hot path that does I/O: does it take ctx and honor cancellation?
• Every goroutine in a pool: does it use the pool's context for shutdown?
• context.Background() in production code is a smell — usually should be a child of a longer-lived context

Tag: [GO-CTX:{loc}:{missing-propagation}]

7. defer Gotchas

• defer in a loop: the deferred function runs when the outer function returns, not when the loop iteration ends. Can accumulate.
• defer with captured variables: closure captures by reference; variables may have changed by the time defer runs.
• defer f(x) evaluates x at defer time; defer func() { f(x) }() evaluates at call time.

Tag: [GO-DEFER:{loc}:{issue}]

8. Integer Overflow

Go doesn't panic on integer overflow (wraps silently). In consensus math, this is dangerous.

Detection:

• Every +, *, - on uint64 / int64 in consensus/fee/stake computation
• Use math.AddUint64 or explicit overflow checks
• big.Int is safer for unbounded arithmetic

Tag: [GO-OVERFLOW:{loc}:{type}]

Output schema

• Language: Go
• Bug class prefix: GO-
• Preferred evidence tags: Same as parent skill

Known bug exemplars (v0.2 — Round 4 verified)

1. btcd signed-int transaction version (CVE-2024-34478) — transaction version treated as signed int instead of unsigned, combined with a data race in the consensus-rule check. Chain split and fund loss possible. Snyk advisory. Skill catch point: Section 8 (integer overflow) + go test -race. Every signed/unsigned mismatch on a consensus-relevant field is a finding.

2. Geth concurrent map iteration and map write panic (issue #17750) — map accessed from multiple goroutines without sync; Go runtime panics with fatal error: concurrent map iteration and map write. go-ethereum #17750. Skill catch point: Section 3 — for every map field on a struct shared across goroutines, verify it is protected by sync.Map, sync.RWMutex, or channel serialization.

3. Cosmos SDK map iteration determinism (EPIC #13039) — class-wide issue across multiple modules. Go's runtime intentionally randomizes range m for map[K]V, making every state-machine iteration over a map a potential chain-halt vector. EPIC #13039. Skill catch point: Section 1 — mandatory check.

4. Aptos 10/18/23 HashMap regression — performance refactor replaced a deterministic map with Rust HashMap; since Aptos uses Move VM written in Rust, this is a Rust concurrency bug by mechanism but the same class applies to Go. Referenced in consensus-safety-invariants skill.

Runtime-gate additional check

Always run go test -race ./... and go vet ./... as part of the language-specific scanner. Race detector findings on consensus-relevant types (state, block, validator-set) are automatic High-severity candidates.

Cross-references

• Supplements all L1 skills when target = Go
• Primary consumer: any depth agent on Go code