Intermittent `CRASH` in `/html/document-isolation-policy/credentialless-cache-storage.https.tentative.window.html?service_worker`

[mukilan]

WPT Run: https://github.com/servo/servo/actions/runs/14115022784/job/39543609628

Backtrace:

Stable unexpected results (1): 
  ▶ CRASH [expected ERROR] /html/document-isolation-policy/credentialless-cache-storage.https.tentative.window.html?service_worker
  │ 
  │ already mutably borrowed: BorrowError (thread Script(1,1), at components/script/dom/bindings/trace.rs:254)
  │    0: servoshell::backtrace::print
  │    1: servoshell::panic_hook::panic_hook
  │    2: std::panicking::rust_panic_with_hook
  │    3: std::panicking::begin_panic_handler::{{closure}}
  │    4: std::sys::backtrace::__rust_end_short_backtrace
  │    5: rust_begin_unwind
  │    6: core::panicking::panic_fmt
  │    7: core::cell::panic_already_mutably_borrowed
  │    8: <script::dom::readablestreamdefaultreader::ReadLoopFulFillmentHandler as mozjs_sys::trace::Traceable>::trace
  │    9: <<script_bindings::root::MaybeUnreflectedDom<T> as script_bindings::root::StableTraceObject>::stable_trace_object::MaybeUnreflectedStackRoot<T> as mozjs_sys::trace::Traceable>::trace
  │   10: script_bindings::root::trace_roots
  │   11: script::script_runtime::trace_rust_roots
  │   12: _ZN2js2gc9GCRuntime18traceRuntimeCommonEP8JSTracerNS1_18TraceOrMarkRuntimeE
  │   13: _ZN2js2gc9GCRuntime22traceRuntimeForMajorGCEP8JSTracerRNS0_13AutoGCSessionE
  │   14: _ZN2js2gc9GCRuntime14beginMarkPhaseERNS0_13AutoGCSessionE
  │   15: _ZN2js2gc9GCRuntime16incrementalSliceERNS_11SliceBudgetEN2JS8GCReasonEb
  │   16: _ZN2js2gc9GCRuntime7gcCycleEbRKNS_11SliceBudgetEN2JS8GCReasonE
  │   17: _ZN2js2gc9GCRuntime7collectEbRKNS_11SliceBudgetEN2JS8GCReasonE
  │   18: _ZN2js2gc9GCRuntime17gcIfRequestedImplEb
  │   19: _ZN2js2gc13CellAllocator17TryNewTenuredCellILNS_7AllowGCE1EEEPvP9JSContextNS0_9AllocKindEm
  │   20: _ZN2js29NewObjectWithGivenTaggedProtoEP9JSContextPK7JSClassN2JS6HandleINS_11TaggedProtoEEENS_2gc9AllocKindENS_13NewObjectKindENS_9EnumFlagsINS_10ObjectFlagEEE
  │   21: script::dom::bindings::codegen::GenericBindings::PromiseNativeHandlerBinding::PromiseNativeHandler_Binding::Wrap
  │   22: script::dom::readablestreamdefaultreader::read_loop
  │   23: <script::dom::readablestreamdefaultreader::ReadLoopFulFillmentHandler as script::dom::promisenativehandler::Callback>::callback
  │   24: script::dom::promise::native_handler_callback
  │   25: _ZN2js23InternalCallOrConstructEP9JSContextRKN2JS8CallArgsENS_14MaybeConstructENS_10CallReasonE
  │   26: _ZN2js4CallEP9JSContextN2JS6HandleINS2_5ValueEEES5_RKNS_13AnyInvokeArgsENS2_13MutableHandleIS4_EENS_10CallReasonE
  │   27: _ZN2js4CallEP9JSContextN2JS6HandleINS2_5ValueEEES5_S5_NS2_13MutableHandleIS4_EE
  │   28: _ZL18PromiseReactionJobP9JSContextjPN2JS5ValueE
  │   29: _ZN2js23InternalCallOrConstructEP9JSContextRKN2JS8CallArgsENS_14MaybeConstructENS_10CallReasonE
  │   30: _ZN2js4CallEP9JSContextN2JS6HandleINS2_5ValueEEES5_RKNS_13AnyInvokeArgsENS2_13MutableHandleIS4_EENS_10CallReasonE
  │   31: _ZN2JS4CallEP9JSContextNS_6HandleINS_5ValueEEES4_RKNS_16HandleValueArrayENS_13MutableHandleIS3_EE
  │   32: script::dom::bindings::codegen::GenericBindings::PromiseBinding::PromiseJobCallback<D>::Call_
  │   33: script::microtask::MicrotaskQueue::checkpoint
  │   34: script::script_thread::ScriptThread::start
  │   35: profile_traits::mem::ProfilerChan::run_with_memory_reporting
  │   36: std::sys::backtrace::__rust_begin_short_backtrace
  │   37: core::ops::function::FnOnce::call_once{{vtable.shim}}
  │   38: std::sys::pal::unix::thread::Thread::new::thread_start
  │   39: <unknown>
  └   40: <unknown>

[mukilan]

@gterzian @Taym95 as this seems to be related to ReadableStreams

[gmorenz]

Pretty sure this is what I just ran into (and fixed) here.

[mrobinson]

@gmorenz Thank you! Once your change lands, we can close this issue.

[sagudev]

Fixed in #36158