Bugzilla

As described in https://phabricator.services.mozilla.com/D20991, the patches in bug 1888429 produce a deadlock involving the Gecko Profiler mutex.

The stacks involved are below, with the first thread waiting on a JS mutex while holding the profiler mutex and the second thread waiting on profiler mutex:
```
PID 5404 | #01: js::GlobalHelperThreadState::wait(js::AutoLockHelperThreadState&, mozilla::BaseTimeDuration<mozilla::TimeDurationValueCalculator>) [js/src/vm/HelperThreads.cpp:924]
PID 5404 | #02: js::GlobalHelperThreadState::cancelOffThreadIonCompile(mozilla::Variant<JSScript*, JS::Zone*, js::ZonesInState, JSRuntime*> const&) [js/src/vm/HelperThreads.cpp:456]
PID 5404 | #03: js::ReleaseAllJITCode(JS::GCContext*) [js/src/gc/GCAPI.cpp:97]
PID 5404 | #04: js::GeckoProfilerRuntime::enable(bool) [js/src/vm/GeckoProfiler.cpp:89]
PID 5404 | #05: mozilla::profiler::ThreadRegistrationLockedRWOnThread::PollJSSampling() [tools/profiler/core/ProfilerThreadRegistrationData.cpp:241]
PID 5404 | #06: locked_profiler_stop(PSAutoLock const&) [tools/profiler/core/platform.cpp:0]
PID 5404 | #07: profiler_stop() [tools/profiler/core/platform.cpp:6647]
PID 5404 | #08: nsProfiler::StopProfiler(JSContext*, mozilla::dom::Promise**) [tools/profiler/gecko/nsProfiler.cpp:181]
PID 5404 | #09: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x383ab76]
PID 5404 | #10: CallMethodHelper::Call() [js/xpconnect/src/XPCWrappedNative.cpp:1174]
PID 5404 | #11: XPCWrappedNative::CallMethod(XPCCallContext&, XPCWrappedNative::CallMode) [js/xpconnect/src/XPCWrappedNative.cpp:1120]
PID 5404 | #12: XPC_WN_CallMethod(JSContext*, unsigned int, JS::Value*) [js/xpconnect/src/XPCWrappedNativeJSOps.cpp:966]
PID 5404 | #13: CallJSNative(JSContext*, bool (*)(JSContext*, unsigned int, JS::Value*), js::CallReason, JS::CallArgs const&) [js/src/vm/Interpreter.cpp:480]
PID 5404 | #14: js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct, js::CallReason) [js/src/vm/Interpreter.cpp:574]
PID 5404 | #15: js::Interpret(JSContext*, js::RunState&) [js/src/vm/Interpreter.cpp:0]
PID 5404 | #16: js::RunScript(JSContext*, js::RunState&) [js/src/vm/Interpreter.cpp:452]
PID 5404 | #17: js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct, js::CallReason) [js/src/vm/Interpreter.cpp:606]
PID 5404 | #18: js::jit::DoCallFallback(JSContext*, js::jit::BaselineFrame*, js::jit::ICFallbackStub*, unsigned int, JS::Value*, JS::MutableHandle<JS::Value>) [js/src/jit/BaselineIC
```

And for the second thread:
```
PSAutoLock::PSAutoLock
ThreadRegistry::Register
ThreadRegistration::ThreadRegistration
ThreadRegistration::RegisterThread
profiler_register_thread
AutoProfilerRegisterThread::AutoProfilerRegisterThread
TaskController::RunPoolThread
```

This can be reproduced on try with the patches in bug 1888429 applied:

`mach try fuzzy -q "'debug 'linux 'xpcshell" tools/profiler/tests/xpcshell`

As described in https://phabricator.services.mozilla.com/D209919, the patches in bug 1888429 produce a deadlock involving the Gecko Profiler mutex.

The stacks involved are below, with the first thread waiting on a JS mutex while holding the profiler mutex and the second thread waiting on profiler mutex:
```
PID 5404 | #01: js::GlobalHelperThreadState::wait(js::AutoLockHelperThreadState&, mozilla::BaseTimeDuration<mozilla::TimeDurationValueCalculator>) [js/src/vm/HelperThreads.cpp:924]
PID 5404 | #02: js::GlobalHelperThreadState::cancelOffThreadIonCompile(mozilla::Variant<JSScript*, JS::Zone*, js::ZonesInState, JSRuntime*> const&) [js/src/vm/HelperThreads.cpp:456]
PID 5404 | #03: js::ReleaseAllJITCode(JS::GCContext*) [js/src/gc/GCAPI.cpp:97]
PID 5404 | #04: js::GeckoProfilerRuntime::enable(bool) [js/src/vm/GeckoProfiler.cpp:89]
PID 5404 | #05: mozilla::profiler::ThreadRegistrationLockedRWOnThread::PollJSSampling() [tools/profiler/core/ProfilerThreadRegistrationData.cpp:241]
PID 5404 | #06: locked_profiler_stop(PSAutoLock const&) [tools/profiler/core/platform.cpp:0]
PID 5404 | #07: profiler_stop() [tools/profiler/core/platform.cpp:6647]
PID 5404 | #08: nsProfiler::StopProfiler(JSContext*, mozilla::dom::Promise**) [tools/profiler/gecko/nsProfiler.cpp:181]
PID 5404 | #09: ??? [/builds/worker/workspace/build/application/firefox/libxul.so + 0x383ab76]
PID 5404 | #10: CallMethodHelper::Call() [js/xpconnect/src/XPCWrappedNative.cpp:1174]
PID 5404 | #11: XPCWrappedNative::CallMethod(XPCCallContext&, XPCWrappedNative::CallMode) [js/xpconnect/src/XPCWrappedNative.cpp:1120]
PID 5404 | #12: XPC_WN_CallMethod(JSContext*, unsigned int, JS::Value*) [js/xpconnect/src/XPCWrappedNativeJSOps.cpp:966]
PID 5404 | #13: CallJSNative(JSContext*, bool (*)(JSContext*, unsigned int, JS::Value*), js::CallReason, JS::CallArgs const&) [js/src/vm/Interpreter.cpp:480]
PID 5404 | #14: js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct, js::CallReason) [js/src/vm/Interpreter.cpp:574]
PID 5404 | #15: js::Interpret(JSContext*, js::RunState&) [js/src/vm/Interpreter.cpp:0]
PID 5404 | #16: js::RunScript(JSContext*, js::RunState&) [js/src/vm/Interpreter.cpp:452]
PID 5404 | #17: js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct, js::CallReason) [js/src/vm/Interpreter.cpp:606]
PID 5404 | #18: js::jit::DoCallFallback(JSContext*, js::jit::BaselineFrame*, js::jit::ICFallbackStub*, unsigned int, JS::Value*, JS::MutableHandle<JS::Value>) [js/src/jit/BaselineIC
```

And for the second thread:
```
PSAutoLock::PSAutoLock
ThreadRegistry::Register
ThreadRegistration::ThreadRegistration
ThreadRegistration::RegisterThread
profiler_register_thread
AutoProfilerRegisterThread::AutoProfilerRegisterThread
TaskController::RunPoolThread
```

This can be reproduced on try with the patches in bug 1888429 applied:

`mach try fuzzy -q "'debug 'linux 'xpcshell" tools/profiler/tests/xpcshell`