client channel: fix TSAN flake in FilterBasedLoadBalancedCall (grpc#32491)

This fixes a very strange TSAN flake seen in an internal test
(b/268292646), which seems to have been introduced in
grpc#32326.

I've included an example of the TSAN failure below, for future
reference. I don't fully understand what is causing this failure. It
looks like the async callback from a previous picker update caused the
pick to be re-queued but then got stuck draining queued callbacks in its
`ExecCtx` instance, while the async callback from the next picker update
had already failed the call. But the part I don't understand is why the
call combiner cancellation callback wound up scheduled on the `ExecCtx`
instance from the first thread -- that seems likely to be caused by
either the `WorkSerializer` or maybe `ExecCtx` work-stealing, but the
exact details are likely to be hard to nail down.

Switching from `EventEngine::Run()` back to `ExecCtx::Run()` seems to
fix the flake, so that's what I'm doing in this PR. I find this
work-around deeply dissatisfying, especially since I do not fully
understand the root cause of the problem. However, given that we are
working toward eliminating the `FilterBasedLoadBalancedCall` code
entirely as part of the promise conversion, this problem is probably not
worth further investigation.

```
WARNING: ThreadSanitizer: data race (pid=7406)
  Read of size 8 at 0x7b8800037558 by thread T47:
    #0 grpc_core::ClientChannel::FilterBasedLoadBalancedCall::~FilterBasedLoadBalancedCall() third_party/grpc/src/core/ext/filters/client_channel/client_channel.cc:2780:5 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x530ed) (BuildId: a8369742d3c435f7f1a244a535f4907c)
    #1 Delete third_party/grpc/src/core/lib/gprpp/ref_counted.h:248:31 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x64a73) (BuildId: a8369742d3c435f7f1a244a535f4907c)
    #2 Unref third_party/grpc/src/core/lib/gprpp/orphanable.h:102:7 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x64a73)
    #3 ~RefCountedPtr third_party/grpc/src/core/lib/gprpp/ref_counted_ptr.h:103:36 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x64a73)
    #4 ~LbQueuedCallCanceller third_party/grpc/src/core/ext/filters/client_channel/client_channel.cc:3132:51 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x64a73)
    #5 grpc_core::ClientChannel::FilterBasedLoadBalancedCall::LbQueuedCallCanceller::CancelLocked(void*, absl::Status) third_party/grpc/src/core/ext/filters/client_channel/client_channel.cc:3168:5 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x64a73)
    #6 exec_ctx_run third_party/grpc/src/core/lib/iomgr/exec_ctx.cc:45:3 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibexec_Uctx.so+0x4199) (BuildId: cafb035b95f6c781e93706a71dce95f3)
    #7 grpc_core::ExecCtx::Flush() third_party/grpc/src/core/lib/iomgr/exec_ctx.cc:72:9 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibexec_Uctx.so+0x4199)
    #8 ~ExecCtx third_party/grpc/src/core/lib/iomgr/exec_ctx.h:117:5 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x6c095) (BuildId: a8369742d3c435f7f1a244a535f4907c)
    #9 operator() third_party/grpc/src/core/ext/filters/client_channel/client_channel.cc:3201:3 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x6c095)
    #10 __invoke<(lambda at third_party/grpc/src/core/ext/filters/client_channel/client_channel.cc:3196:46) &> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:394:23 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x6c095)
    #11 invoke<(lambda at third_party/grpc/src/core/ext/filters/client_channel/client_channel.cc:3196:46) &> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:539:12 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x6c095)
    #12 InvokeR<void, (lambda at third_party/grpc/src/core/ext/filters/client_channel/client_channel.cc:3196:46) &, void> third_party/absl/functional/internal/any_invocable.h:131:3 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x6c095)
    #13 void absl::internal_any_invocable::LocalInvoker<false, void, grpc_core::ClientChannel::FilterBasedLoadBalancedCall::RetryPickLocked()::$_0&>(absl::internal_any_invocable::TypeErasedState*) third_party/absl/functional/internal/any_invocable.h:301:10 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x6c095)
    #14 operator() third_party/absl/functional/internal/any_invocable.h:855:1 (libST-a5842b3303c3_net_Sgrpc_Sinternal_Ssrc_Score_Sext_Sevent_Uengine_Slibevent_Uengine_Uem_Uimpl.so+0x16a74) (BuildId: 7802a789e61dddac5a33230a2f294046)
    #15 util::functional::internal::FunctorCallback<Closure, false, absl::AnyInvocable<void ()>, void ()>::Run() util/functional/to_callback_internal.h:87:27 (libST-a5842b3303c3_net_Sgrpc_Sinternal_Ssrc_Score_Sext_Sevent_Uengine_Slibevent_Uengine_Uem_Uimpl.so+0x16a74)
    #16 void eventmanager::EventManager::RunTask<false>(eventmanager::EventManager::WorkerThread*, eventmanager::TaskInfo*) net/eventmanager/em1/eventmanager.cc:2464:20 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x2ae1b) (BuildId: b3d97518d96e160722658c4aa0795013)
    #17 void eventmanager::EventManager::RunWorkerLoop<false, false>(eventmanager::EventManager::WorkerThread*) net/eventmanager/em1/eventmanager.cc (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x2a45d) (BuildId: b3d97518d96e160722658c4aa0795013)
    #18 eventmanager::EventManager::WorkerThread::WorkerMain() net/eventmanager/em1/eventmanager.cc:430:19 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x1d841) (BuildId: b3d97518d96e160722658c4aa0795013)
    #19 operator() net/eventmanager/em1/eventmanager.cc:396:64 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x28351) (BuildId: b3d97518d96e160722658c4aa0795013)
    #20 __invoke<(lambda at net/eventmanager/em1/eventmanager.cc:396:55)> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:394:23 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x28351)
    #21 invoke<(lambda at net/eventmanager/em1/eventmanager.cc:396:55)> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:539:12 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x28351)
    #22 InvokeR<void, (lambda at net/eventmanager/em1/eventmanager.cc:396:55), void> third_party/absl/functional/internal/any_invocable.h:131:3 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x28351)
    #23 void absl::internal_any_invocable::LocalInvoker<false, void, eventmanager::EventManager::WorkerThread::StartThread(int, int, thread::SchedPolicy, std::__tsan::basic_string_view<char, std::__tsan::char_traits<char>>)::'lambda'()&&>(absl::internal_any_invocable::TypeErasedState*) third_party/absl/functional/internal/any_invocable.h:301:10 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x28351)
    #24 operator() third_party/absl/functional/internal/any_invocable.h:863:1 (libST-a5842b3303c3_security_Sganpati_Ssharded_Uclient_Slibacl_Ucache.so+0x24c1e) (BuildId: a86eb59aee0be7b5882a1b532922e3ca)
    #25 ClosureThread::Run() thread/thread.h:459:25 (libST-a5842b3303c3_security_Sganpati_Ssharded_Uclient_Slibacl_Ucache.so+0x24c1e)
    #26 Thread::ThreadBody(void*) thread/thread.cc:1284:16 (libST-a5842b3303c3_thread_Slibthread.so+0x251e9) (BuildId: a1762ef5c5732b3ad8a3b3d798292e27)

  Previous write of size 8 at 0x7b8800037558 by thread T40:
    #0 grpc_core::ClientChannel::FilterBasedLoadBalancedCall::PendingBatchesFail(absl::Status, bool (*)(grpc_core::CallCombinerClosureList const&)) third_party/grpc/src/core/ext/filters/client_channel/client_channel.cc:2863:13 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x537c7) (BuildId: a8369742d3c435f7f1a244a535f4907c)
    #1 grpc_core::ClientChannel::FilterBasedLoadBalancedCall::TryPick(bool) third_party/grpc/src/core/ext/filters/client_channel/client_channel.cc:3179:7 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x5537f) (BuildId: a8369742d3c435f7f1a244a535f4907c)
    #2 operator() third_party/grpc/src/core/ext/filters/client_channel/client_channel.cc:3200:5 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x6c077) (BuildId: a8369742d3c435f7f1a244a535f4907c)
    #3 __invoke<(lambda at third_party/grpc/src/core/ext/filters/client_channel/client_channel.cc:3196:46) &> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:394:23 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x6c077)
    #4 invoke<(lambda at third_party/grpc/src/core/ext/filters/client_channel/client_channel.cc:3196:46) &> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:539:12 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x6c077)
    #5 InvokeR<void, (lambda at third_party/grpc/src/core/ext/filters/client_channel/client_channel.cc:3196:46) &, void> third_party/absl/functional/internal/any_invocable.h:131:3 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x6c077)
    #6 void absl::internal_any_invocable::LocalInvoker<false, void, grpc_core::ClientChannel::FilterBasedLoadBalancedCall::RetryPickLocked()::$_0&>(absl::internal_any_invocable::TypeErasedState*) third_party/absl/functional/internal/any_invocable.h:301:10 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Uclient_Uchannel.so+0x6c077)
    #7 operator() third_party/absl/functional/internal/any_invocable.h:855:1 (libST-a5842b3303c3_net_Sgrpc_Sinternal_Ssrc_Score_Sext_Sevent_Uengine_Slibevent_Uengine_Uem_Uimpl.so+0x16a74) (BuildId: 7802a789e61dddac5a33230a2f294046)
    #8 util::functional::internal::FunctorCallback<Closure, false, absl::AnyInvocable<void ()>, void ()>::Run() util/functional/to_callback_internal.h:87:27 (libST-a5842b3303c3_net_Sgrpc_Sinternal_Ssrc_Score_Sext_Sevent_Uengine_Slibevent_Uengine_Uem_Uimpl.so+0x16a74)
    #9 void eventmanager::EventManager::RunTask<false>(eventmanager::EventManager::WorkerThread*, eventmanager::TaskInfo*) net/eventmanager/em1/eventmanager.cc:2464:20 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x2ae1b) (BuildId: b3d97518d96e160722658c4aa0795013)
    #10 void eventmanager::EventManager::RunWorkerLoop<false, false>(eventmanager::EventManager::WorkerThread*) net/eventmanager/em1/eventmanager.cc (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x2a45d) (BuildId: b3d97518d96e160722658c4aa0795013)
    #11 eventmanager::EventManager::WorkerThread::WorkerMain() net/eventmanager/em1/eventmanager.cc:430:19 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x1d841) (BuildId: b3d97518d96e160722658c4aa0795013)
    #12 operator() net/eventmanager/em1/eventmanager.cc:396:64 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x28351) (BuildId: b3d97518d96e160722658c4aa0795013)
    #13 __invoke<(lambda at net/eventmanager/em1/eventmanager.cc:396:55)> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:394:23 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x28351)
    #14 invoke<(lambda at net/eventmanager/em1/eventmanager.cc:396:55)> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:539:12 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x28351)
    #15 InvokeR<void, (lambda at net/eventmanager/em1/eventmanager.cc:396:55), void> third_party/absl/functional/internal/any_invocable.h:131:3 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x28351)
    #16 void absl::internal_any_invocable::LocalInvoker<false, void, eventmanager::EventManager::WorkerThread::StartThread(int, int, thread::SchedPolicy, std::__tsan::basic_string_view<char, std::__tsan::char_traits<char>>)::'lambda'()&&>(absl::internal_any_invocable::TypeErasedState*) third_party/absl/functional/internal/any_invocable.h:301:10 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x28351)
    #17 operator() third_party/absl/functional/internal/any_invocable.h:863:1 (libST-a5842b3303c3_security_Sganpati_Ssharded_Uclient_Slibacl_Ucache.so+0x24c1e) (BuildId: a86eb59aee0be7b5882a1b532922e3ca)
    #18 ClosureThread::Run() thread/thread.h:459:25 (libST-a5842b3303c3_security_Sganpati_Ssharded_Uclient_Slibacl_Ucache.so+0x24c1e)
    #19 Thread::ThreadBody(void*) thread/thread.cc:1284:16 (libST-a5842b3303c3_thread_Slibthread.so+0x251e9) (BuildId: a1762ef5c5732b3ad8a3b3d798292e27)

  Thread T47 'EventManager_Default' (tid=7454, running) created by main thread at:
    #0 pthread_create third_party/llvm/llvm-project/compiler-rt/lib/tsan/rtl/tsan_interceptors_posix.cpp:1048:3 (c0da98875dfb74bd2cfcbd76306f382f2d05e1326f778b3a4cefdef1a42a75e7_020000b94930+0x1887b9) (BuildId: e468d94e410a7e13e19b26c4f7277674)
    #1 Thread::CreatePthread(pthread_attr_t&) thread/thread.cc:485:13 (libST-a5842b3303c3_thread_Slibthread.so+0x24b1d) (BuildId: a1762ef5c5732b3ad8a3b3d798292e27)
    #2 Thread::Start() thread/thread.cc:667:3 (libST-a5842b3303c3_thread_Slibthread.so+0x2574b) (BuildId: a1762ef5c5732b3ad8a3b3d798292e27)
    #3 StartThread net/eventmanager/em1/eventmanager.cc:397:14 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x1bbed) (BuildId: b3d97518d96e160722658c4aa0795013)
    #4 eventmanager::EventManager::EventManager(eventmanager::EventManager::Options const&) net/eventmanager/em1/eventmanager.cc:1274:23 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x1bbed)
    #5 InitializeDefaultEventManager() net/eventmanager/em1/eventmanager.cc:3042:39 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x25c06) (BuildId: b3d97518d96e160722658c4aa0795013)
    #6 __invoke<void (*&)()> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:394:23 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9) (BuildId: fe43c5a995ecc22efa243d05ef607fb9)
    #7 invoke<void (*&)()> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:539:12 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9)
    #8 void absl::base_internal::CallOnceImpl<void (*&)()>(std::__tsan::atomic<unsigned int>*, absl::base_internal::SchedulingMode, void (*&)()) third_party/absl/base/call_once.h:184:5 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9)
    #9 GoogleOnceInternalInit base/once.cc:23:5 (libST-a5842b3303c3_base_Slibonce.so+0xeee) (BuildId: 6c436371e89d7962c2b544d27465d6a0)
    #10 GoogleOnceInternalInitSchedCoopAndKernel(std::__tsan::atomic<unsigned int>*, void (*)()) base/once.cc:15:3 (libST-a5842b3303c3_base_Slibonce.so+0xeee)
    #11 GoogleOnceInit base/once.h:72:5 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x25ad9) (BuildId: b3d97518d96e160722658c4aa0795013)
    #12 eventmanager::EventManager::DefaultEventManager() net/eventmanager/em1/eventmanager.cc:3059:3 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x25ad9)
    #13 Default net/eventmanager/em1/eventmanager.h:780:43 (libST-a5842b3303c3_net_Seventmanager_Slibeventmanager_Udefault.so+0x14c5) (BuildId: 2e1dde05e8bce5319856279d896c4405)
    #14 eventmanager::Default() net/eventmanager/eventmanager_default.cc:22:10 (libST-a5842b3303c3_net_Seventmanager_Slibeventmanager_Udefault.so+0x14c5)
    #15 grpc::(anonymous namespace)::InitGlobalEventManager() net/grpc/internal/src/core/ext/event_engine/grpc_event_manager.cc:38:23 (libST-a5842b3303c3_net_Sgrpc_Sinternal_Ssrc_Score_Sext_Sevent_Uengine_Slibgrpc_Uevent_Umanager.so+0x1c28) (BuildId: 8bd3c1826fd11ffa128e7839a85c05a0)
    #16 __invoke<void (*&)()> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:394:23 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9) (BuildId: fe43c5a995ecc22efa243d05ef607fb9)
    #17 invoke<void (*&)()> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:539:12 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9)
    #18 void absl::base_internal::CallOnceImpl<void (*&)()>(std::__tsan::atomic<unsigned int>*, absl::base_internal::SchedulingMode, void (*&)()) third_party/absl/base/call_once.h:184:5 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9)
    #19 call_once<void (*&)()> third_party/absl/base/call_once.h:216:5 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaa0b) (BuildId: fe43c5a995ecc22efa243d05ef607fb9)
    #20 gpr_once_init third_party/grpc/src/core/lib/gpr/sync_abseil.cc:107:3 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaa0b)
    #21 grpc::GetGrpcEventManager() net/grpc/internal/src/core/ext/event_engine/grpc_event_manager.cc:51:3 (libST-a5842b3303c3_net_Sgrpc_Sinternal_Ssrc_Score_Sext_Sevent_Uengine_Slibgrpc_Uevent_Umanager.so+0x18c1) (BuildId: 8bd3c1826fd11ffa128e7839a85c05a0)
    #22 check_engine_available(bool) net/grpc/internal/src/core/ext/poller/event_manager_poller/ev_event_manager_linux.cc:1271:21 (libST-a5842b3303c3_net_Sgrpc_Sinternal_Ssrc_Score_Sext_Spoller_Sevent_Umanager_Upoller_Slibev_Uevent_Umanager_Ulinux.so+0x4fcb) (BuildId: 620adb83259aed32440614774678b3a1)
    #23 try_engine third_party/grpc/src/core/lib/iomgr/ev_posix.cc:141:9 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Ubase.so+0xad888) (BuildId: 3cb6b043bd10222927301e33a3760646)
    #24 operator() third_party/grpc/src/core/lib/iomgr/ev_posix.cc:184:7 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Ubase.so+0xad888)
    #25 grpc_event_engine_init()::$_0::__invoke() third_party/grpc/src/core/lib/iomgr/ev_posix.cc:175:35 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Ubase.so+0xad888)
    #26 __invoke<void (*&)()> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:394:23 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9) (BuildId: fe43c5a995ecc22efa243d05ef607fb9)
    #27 invoke<void (*&)()> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:539:12 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9)
    #28 void absl::base_internal::CallOnceImpl<void (*&)()>(std::__tsan::atomic<unsigned int>*, absl::base_internal::SchedulingMode, void (*&)()) third_party/absl/base/call_once.h:184:5 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9)
    #29 call_once<void (*&)()> third_party/absl/base/call_once.h:216:5 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaa0b) (BuildId: fe43c5a995ecc22efa243d05ef607fb9)
    #30 gpr_once_init third_party/grpc/src/core/lib/gpr/sync_abseil.cc:107:3 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaa0b)
    #31 grpc_event_engine_init() third_party/grpc/src/core/lib/iomgr/ev_posix.cc:175:3 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Ubase.so+0xacab1) (BuildId: 3cb6b043bd10222927301e33a3760646)
    grpc#32 iomgr_platform_init() third_party/grpc/src/core/lib/iomgr/iomgr_posix.cc:43:3 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Ubase.so+0xaf1d0) (BuildId: 3cb6b043bd10222927301e33a3760646)
    grpc#33 grpc_iomgr_platform_init() third_party/grpc/src/core/lib/iomgr/iomgr_internal.cc:35:35 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibexec_Uctx.so+0x688b) (BuildId: cafb035b95f6c781e93706a71dce95f3)
    grpc#34 grpc_iomgr_init() third_party/grpc/src/core/lib/iomgr/iomgr.cc:66:3 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Ubase.so+0xae777) (BuildId: 3cb6b043bd10222927301e33a3760646)
    grpc#35 grpc_init third_party/grpc/src/core/lib/surface/init.cc:144:5 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc.so+0x4518) (BuildId: 778b43e2e8f8c132a7acf9b3da117fff)
    grpc#36 k3::(anonymous namespace)::GrpcInitHackEnvironment::SetUp() storage/k3/grpc/grpc_server_test.cc:144:27 (c0da98875dfb74bd2cfcbd76306f382f2d05e1326f778b3a4cefdef1a42a75e7_020000b94930+0x212d21) (BuildId: e468d94e410a7e13e19b26c4f7277674)
    grpc#37 SetUpEnvironment third_party/googletest/googletest/src/gtest.cc:5763:55 (libST-a5842b3303c3_third_Uparty_Sgoogletest_Slibgtest.so+0x6f58b) (BuildId: ec51e8d56b1390e9939f663d4700c7da)
    grpc#38 for_each<std::__tsan::__wrap_iter<testing::Environment *const *>, void (*)(testing::Environment *)> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__algorithm/for_each.h:26:5 (libST-a5842b3303c3_third_Uparty_Sgoogletest_Slibgtest.so+0x6f58b)
    grpc#39 ForEach<std::__tsan::vector<testing::Environment *, std::__tsan::allocator<testing::Environment *> >, void (*)(testing::Environment *)> third_party/googletest/googletest/src/gtest-internal-inl.h:288:3 (libST-a5842b3303c3_third_Uparty_Sgoogletest_Slibgtest.so+0x6f58b)
    grpc#40 testing::internal::UnitTestImpl::RunAllTests() third_party/googletest/googletest/src/gtest.cc:5876:9 (libST-a5842b3303c3_third_Uparty_Sgoogletest_Slibgtest.so+0x6f58b)
    grpc#41 HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool> third_party/googletest/googletest/src/gtest.cc (libST-a5842b3303c3_third_Uparty_Sgoogletest_Slibgtest.so+0x6ee41) (BuildId: ec51e8d56b1390e9939f663d4700c7da)
    grpc#42 testing::UnitTest::Run() third_party/googletest/googletest/src/gtest.cc:5464:10 (libST-a5842b3303c3_third_Uparty_Sgoogletest_Slibgtest.so+0x6ee41)
    grpc#43 RUN_ALL_TESTS third_party/googletest/googletest/include/gtest/gtest.h:2329:73 (c0da98875dfb74bd2cfcbd76306f382f2d05e1326f778b3a4cefdef1a42a75e7_020000b94930+0x2aa83a) (BuildId: e468d94e410a7e13e19b26c4f7277674)
    grpc#44 main testing/base/internal/gunit_main.cc:86:10 (c0da98875dfb74bd2cfcbd76306f382f2d05e1326f778b3a4cefdef1a42a75e7_020000b94930+0x2aa83a)

  Thread T40 'EventManager_Default' (tid=7447, running) created by main thread at:
    #0 pthread_create third_party/llvm/llvm-project/compiler-rt/lib/tsan/rtl/tsan_interceptors_posix.cpp:1048:3 (c0da98875dfb74bd2cfcbd76306f382f2d05e1326f778b3a4cefdef1a42a75e7_020000b94930+0x1887b9) (BuildId: e468d94e410a7e13e19b26c4f7277674)
    #1 Thread::CreatePthread(pthread_attr_t&) thread/thread.cc:485:13 (libST-a5842b3303c3_thread_Slibthread.so+0x24b1d) (BuildId: a1762ef5c5732b3ad8a3b3d798292e27)
    #2 Thread::Start() thread/thread.cc:667:3 (libST-a5842b3303c3_thread_Slibthread.so+0x2574b) (BuildId: a1762ef5c5732b3ad8a3b3d798292e27)
    #3 StartThread net/eventmanager/em1/eventmanager.cc:397:14 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x1bbed) (BuildId: b3d97518d96e160722658c4aa0795013)
    #4 eventmanager::EventManager::EventManager(eventmanager::EventManager::Options const&) net/eventmanager/em1/eventmanager.cc:1274:23 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x1bbed)
    #5 InitializeDefaultEventManager() net/eventmanager/em1/eventmanager.cc:3042:39 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x25c06) (BuildId: b3d97518d96e160722658c4aa0795013)
    #6 __invoke<void (*&)()> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:394:23 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9) (BuildId: fe43c5a995ecc22efa243d05ef607fb9)
    #7 invoke<void (*&)()> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:539:12 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9)
    #8 void absl::base_internal::CallOnceImpl<void (*&)()>(std::__tsan::atomic<unsigned int>*, absl::base_internal::SchedulingMode, void (*&)()) third_party/absl/base/call_once.h:184:5 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9)
    #9 GoogleOnceInternalInit base/once.cc:23:5 (libST-a5842b3303c3_base_Slibonce.so+0xeee) (BuildId: 6c436371e89d7962c2b544d27465d6a0)
    #10 GoogleOnceInternalInitSchedCoopAndKernel(std::__tsan::atomic<unsigned int>*, void (*)()) base/once.cc:15:3 (libST-a5842b3303c3_base_Slibonce.so+0xeee)
    #11 GoogleOnceInit base/once.h:72:5 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x25ad9) (BuildId: b3d97518d96e160722658c4aa0795013)
    #12 eventmanager::EventManager::DefaultEventManager() net/eventmanager/em1/eventmanager.cc:3059:3 (libST-a5842b3303c3_net_Seventmanager_Sem1_Slibem1.so+0x25ad9)
    #13 Default net/eventmanager/em1/eventmanager.h:780:43 (libST-a5842b3303c3_net_Seventmanager_Slibeventmanager_Udefault.so+0x14c5) (BuildId: 2e1dde05e8bce5319856279d896c4405)
    #14 eventmanager::Default() net/eventmanager/eventmanager_default.cc:22:10 (libST-a5842b3303c3_net_Seventmanager_Slibeventmanager_Udefault.so+0x14c5)
    #15 grpc::(anonymous namespace)::InitGlobalEventManager() net/grpc/internal/src/core/ext/event_engine/grpc_event_manager.cc:38:23 (libST-a5842b3303c3_net_Sgrpc_Sinternal_Ssrc_Score_Sext_Sevent_Uengine_Slibgrpc_Uevent_Umanager.so+0x1c28) (BuildId: 8bd3c1826fd11ffa128e7839a85c05a0)
    #16 __invoke<void (*&)()> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:394:23 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9) (BuildId: fe43c5a995ecc22efa243d05ef607fb9)
    #17 invoke<void (*&)()> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:539:12 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9)
    #18 void absl::base_internal::CallOnceImpl<void (*&)()>(std::__tsan::atomic<unsigned int>*, absl::base_internal::SchedulingMode, void (*&)()) third_party/absl/base/call_once.h:184:5 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9)
    #19 call_once<void (*&)()> third_party/absl/base/call_once.h:216:5 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaa0b) (BuildId: fe43c5a995ecc22efa243d05ef607fb9)
    #20 gpr_once_init third_party/grpc/src/core/lib/gpr/sync_abseil.cc:107:3 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaa0b)
    #21 grpc::GetGrpcEventManager() net/grpc/internal/src/core/ext/event_engine/grpc_event_manager.cc:51:3 (libST-a5842b3303c3_net_Sgrpc_Sinternal_Ssrc_Score_Sext_Sevent_Uengine_Slibgrpc_Uevent_Umanager.so+0x18c1) (BuildId: 8bd3c1826fd11ffa128e7839a85c05a0)
    #22 check_engine_available(bool) net/grpc/internal/src/core/ext/poller/event_manager_poller/ev_event_manager_linux.cc:1271:21 (libST-a5842b3303c3_net_Sgrpc_Sinternal_Ssrc_Score_Sext_Spoller_Sevent_Umanager_Upoller_Slibev_Uevent_Umanager_Ulinux.so+0x4fcb) (BuildId: 620adb83259aed32440614774678b3a1)
    #23 try_engine third_party/grpc/src/core/lib/iomgr/ev_posix.cc:141:9 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Ubase.so+0xad888) (BuildId: 3cb6b043bd10222927301e33a3760646)
    #24 operator() third_party/grpc/src/core/lib/iomgr/ev_posix.cc:184:7 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Ubase.so+0xad888)
    #25 grpc_event_engine_init()::$_0::__invoke() third_party/grpc/src/core/lib/iomgr/ev_posix.cc:175:35 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Ubase.so+0xad888)
    #26 __invoke<void (*&)()> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:394:23 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9) (BuildId: fe43c5a995ecc22efa243d05ef607fb9)
    #27 invoke<void (*&)()> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__functional/invoke.h:539:12 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9)
    #28 void absl::base_internal::CallOnceImpl<void (*&)()>(std::__tsan::atomic<unsigned int>*, absl::base_internal::SchedulingMode, void (*&)()) third_party/absl/base/call_once.h:184:5 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaab9)
    #29 call_once<void (*&)()> third_party/absl/base/call_once.h:216:5 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaa0b) (BuildId: fe43c5a995ecc22efa243d05ef607fb9)
    #30 gpr_once_init third_party/grpc/src/core/lib/gpr/sync_abseil.cc:107:3 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgpr.so+0xaa0b)
    #31 grpc_event_engine_init() third_party/grpc/src/core/lib/iomgr/ev_posix.cc:175:3 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Ubase.so+0xacab1) (BuildId: 3cb6b043bd10222927301e33a3760646)
    grpc#32 iomgr_platform_init() third_party/grpc/src/core/lib/iomgr/iomgr_posix.cc:43:3 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Ubase.so+0xaf1d0) (BuildId: 3cb6b043bd10222927301e33a3760646)
    grpc#33 grpc_iomgr_platform_init() third_party/grpc/src/core/lib/iomgr/iomgr_internal.cc:35:35 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibexec_Uctx.so+0x688b) (BuildId: cafb035b95f6c781e93706a71dce95f3)
    grpc#34 grpc_iomgr_init() third_party/grpc/src/core/lib/iomgr/iomgr.cc:66:3 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc_Ubase.so+0xae777) (BuildId: 3cb6b043bd10222927301e33a3760646)
    grpc#35 grpc_init third_party/grpc/src/core/lib/surface/init.cc:144:5 (libST-a5842b3303c3_third_Uparty_Sgrpc_Sgoogle_Slibgrpc.so+0x4518) (BuildId: 778b43e2e8f8c132a7acf9b3da117fff)
    grpc#36 k3::(anonymous namespace)::GrpcInitHackEnvironment::SetUp() storage/k3/grpc/grpc_server_test.cc:144:27 (c0da98875dfb74bd2cfcbd76306f382f2d05e1326f778b3a4cefdef1a42a75e7_020000b94930+0x212d21) (BuildId: e468d94e410a7e13e19b26c4f7277674)
    grpc#37 SetUpEnvironment third_party/googletest/googletest/src/gtest.cc:5763:55 (libST-a5842b3303c3_third_Uparty_Sgoogletest_Slibgtest.so+0x6f58b) (BuildId: ec51e8d56b1390e9939f663d4700c7da)
    grpc#38 for_each<std::__tsan::__wrap_iter<testing::Environment *const *>, void (*)(testing::Environment *)> third_party/crosstool/v18/stable/toolchain/bin/../include/c++/v1/__algorithm/for_each.h:26:5 (libST-a5842b3303c3_third_Uparty_Sgoogletest_Slibgtest.so+0x6f58b)
    grpc#39 ForEach<std::__tsan::vector<testing::Environment *, std::__tsan::allocator<testing::Environment *> >, void (*)(testing::Environment *)> third_party/googletest/googletest/src/gtest-internal-inl.h:288:3 (libST-a5842b3303c3_third_Uparty_Sgoogletest_Slibgtest.so+0x6f58b)
    grpc#40 testing::internal::UnitTestImpl::RunAllTests() third_party/googletest/googletest/src/gtest.cc:5876:9 (libST-a5842b3303c3_third_Uparty_Sgoogletest_Slibgtest.so+0x6f58b)
    grpc#41 HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool> third_party/googletest/googletest/src/gtest.cc (libST-a5842b3303c3_third_Uparty_Sgoogletest_Slibgtest.so+0x6ee41) (BuildId: ec51e8d56b1390e9939f663d4700c7da)
    grpc#42 testing::UnitTest::Run() third_party/googletest/googletest/src/gtest.cc:5464:10 (libST-a5842b3303c3_third_Uparty_Sgoogletest_Slibgtest.so+0x6ee41)
    grpc#43 RUN_ALL_TESTS third_party/googletest/googletest/include/gtest/gtest.h:2329:73 (c0da98875dfb74bd2cfcbd76306f382f2d05e1326f778b3a4cefdef1a42a75e7_020000b94930+0x2aa83a) (BuildId: e468d94e410a7e13e19b26c4f7277674)
    grpc#44 main testing/base/internal/gunit_main.cc:86:10 (c0da98875dfb74bd2cfcbd76306f382f2d05e1326f778b3a4cefdef1a42a75e7_020000b94930+0x2aa83a)

SUMMARY: ThreadSanitizer: data race third_party/grpc/src/core/ext/filters/client_channel/client_channel.cc:2780:5 in grpc_core::ClientChannel::FilterBasedLoadBalancedCall::~FilterBasedLoadBalancedCall()
```

Author: markdroth

src/core/ext/filters/client_channel/client_channel.cc

@@ -3192,11 +3192,28 @@ void ClientChannel::FilterBasedLoadBalancedCall::RetryPickLocked() {
   lb_call_canceller_ = nullptr;
   // Do an async callback to resume call processing, so that we're not
   // doing it while holding the channel's LB mutex.
-  chand()->owning_stack_->EventEngine()->Run([this]() {
-    ApplicationCallbackExecCtx application_exec_ctx;
-    ExecCtx exec_ctx;
-    TryPick(/*was_queued=*/true);
-  });
+  // TODO(roth): We should really be using EventEngine::Run() here
+  // instead of ExecCtx::Run().  Unfortunately, doing that seems to cause
+  // a flaky TSAN failure for reasons that I do not fully understand.
+  // However, given that we are working toward eliminating this code as
+  // part of the promise conversion, it doesn't seem worth further
+  // investigation right now.
+  ExecCtx::Run(DEBUG_LOCATION, NewClosure([this](grpc_error_handle) {
+                 // If there are a lot of queued calls here, resuming them
+                 // all may cause us to stay inside C-core for a long period
+                 // of time. All of that work would be done using the same
+                 // ExecCtx instance and therefore the same cached value of
+                 // "now". The longer it takes to finish all of this work
+                 // and exit from C-core, the more stale the cached value of
+                 // "now" may become. This can cause problems whereby (e.g.)
+                 // we calculate a timer deadline based on the stale value,
+                 // which results in the timer firing too early. To avoid
+                 // this, we invalidate the cached value for each call we
+                 // process.
+                 ExecCtx::Get()->InvalidateNow();
+                 TryPick(/*was_queued=*/true);
+               }),
+               absl::OkStatus());
 }
 
 void ClientChannel::FilterBasedLoadBalancedCall::CreateSubchannelCall() {