withDiscardingTaskGroup cancelAll crash

[KeithBauerANZ]

Description

Occasionally, calling cancelAll on a DiscardingTaskGroup will crash.

Reproduction

var i = 0
while true {
    print("\(i)")
    await withDiscardingTaskGroup { group in
        group.addTask {
            _ = try? await Task.sleep(nanoseconds: .max / 2)
        }

        group.cancelAll()
    }
    i += 1
}

swiftc -swift-version 6 TaskGroupCancelAllCrash.swift && lldb ./TaskGroupCancelAllCrash
r
...
1830090
Process 87524 stopped
* thread #4, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x8)
    frame #0: 0x00000002654ded1c libswift_Concurrency.dylib`withStatusRecordLock(swift::AsyncTask*, swift::ActiveTaskStatus, __swift::__runtime::llvm::function_ref<void (swift::ActiveTaskStatus)>, __swift::__runtime::llvm::function_ref<void (swift::ActiveTaskStatus, swift::ActiveTaskStatus&)>) + 396
libswift_Concurrency.dylib`withStatusRecordLock:
->  0x2654ded1c <+396>: ldr    x9, [x27, #0x8]
    0x2654ded20 <+400>: orr    x8, x8, x28, lsl #32
    0x2654ded24 <+404>: stp    x8, x9, [sp, #0x20]
    0x2654ded28 <+408>: cbz    x21, 0x2654ded40 ; <+432>
Target 0: (TaskGroupCancelAllCrash) stopped.

Stack dump

(lldb) bt all
  thread #2
    frame #0: 0x0000000184bc0ba4 libsystem_kernel.dylib`__workq_kernreturn + 8
  thread #3
    frame #0: 0x0000000184bc6684 libsystem_kernel.dylib`__sigsuspend_nocancel + 8
    frame #1: 0x0000000184a60c64 libdispatch.dylib`_dispatch_sigsuspend + 48
    frame #2: 0x0000000184a60c34 libdispatch.dylib`_dispatch_sig_thread + 60
* thread #4, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x8)
  * frame #0: 0x00000002654ded1c libswift_Concurrency.dylib`withStatusRecordLock(swift::AsyncTask*, swift::ActiveTaskStatus, __swift::__runtime::llvm::function_ref<void (swift::ActiveTaskStatus)>, __swift::__runtime::llvm::function_ref<void (swift::ActiveTaskStatus, swift::ActiveTaskStatus&)>) + 396
    frame #1: 0x00000002654df7b8 libswift_Concurrency.dylib`swift_task_cancelImpl(swift::AsyncTask*) + 216
    frame #2: 0x00000002654e12d8 libswift_Concurrency.dylib`swift_taskGroup_cancelAll + 144
    frame #3: 0x0000000100001270 TaskGroupCancelAllCrash`(1) suspend resume partial function for closure #1 (inout Swift.DiscardingTaskGroup) async -> () in TaskGroupCancelAllCrash + 112
    frame #4: 0x00000002654a50d0 libswift_Concurrency.dylib`(2) await resume partial function for Swift.withDiscardingTaskGroup<τ_0_0>(returning: τ_0_0.Type, isolation: isolated Swift.Optional<Swift.Actor>, body: (inout Swift.DiscardingTaskGroup) async -> τ_0_0) async -> τ_0_0
    frame #5: 0x0000000100000b60 TaskGroupCancelAllCrash`async_MainTQ0_
    frame #6: 0x0000000100000f30 TaskGroupCancelAllCrash`(1) await resume partial function for reabstraction thunk helper from @escaping @convention(thin) @async () -> () to @escaping @callee_guaranteed @async () -> (@out (), @error @owned Swift.Error)
    frame #7: 0x0000000100001058 TaskGroupCancelAllCrash`(1) await resume partial function for partial apply forwarder for reabstraction thunk helper from @escaping @convention(thin) @async () -> () to @escaping @callee_guaranteed @async () -> (@out (), @error @owned Swift.Error)
  thread #5
    frame #0: 0x0000000184bc0ba4 libsystem_kernel.dylib`__workq_kernreturn + 8
  thread #6
    frame #0: 0x0000000184bc0ba4 libsystem_kernel.dylib`__workq_kernreturn + 8

Expected behavior

Not… crash

Environment

 swiftc -version
swift-driver version: 1.120.5 Apple Swift version 6.1 (swiftlang-6.1.0.110.21 clang-1700.0.13.3)
Target: arm64-apple-macosx15.0

Additional information

No response

[mikeash]

This should be fixed by #80096.