TSan warning about isFiberRunning reading a stale pointer

[vadimskipin]

TSan reports a problem in one of our tests:

WARNING: ThreadSanitizer: data race (pid=40521)
  Write of size 8 at 0xff12bac3ee88 by thread T430:
    #0 operator delete(void*, unsigned long, std::align_val_t) <null> (amber-storage-bench+0x104748) (BuildId: 724e2958dfce8c8c5b51a12a902811a05da08c68)
    #1 std::default_delete<silk::Fiber>::operator()(silk::Fiber*) const /usr/lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/unique_ptr.h:99:2 (amber-storage-bench+0x18a804) (BuildId: 724e2958dfce8c8c5b51a12a902811a05da08c68)
    #2 std::unique_ptr<silk::Fiber, std::default_delete<silk::Fiber>>::~unique_ptr() /usr/lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/unique_ptr.h:404:4 (amber-storage-bench+0x18a804)
    #3 __call_tls_dtors stdlib/cxa_thread_atexit_impl.c:159:7 (libc.so.6+0x3d7d4) (BuildId: 4a81130bc30ded618f1edc030ecc5439e066dc68)

  Previous atomic read of size 1 at 0xff12bac3ee88 by thread T438:
    #0 std::atomic<silk::FiberState>::load(std::memory_order) const /usr/lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/atomic:297:2 (amber-storage-bench+0x184160) (BuildId: 724e2958dfce8c8c5b51a12a902811a05da08c68)
    #1 silk::FiberScheduler::isFiberRunning(silk::Fiber*) contrib/silk/src/fibers/fiber.cpp:1444:25 (amber-storage-bench+0x184160)
    #2 silk::FiberMutex::lockSlow(silk::FiberMutex::State, unsigned long*) contrib/silk/src/fibers/mutex.cpp:40:42 (amber-storage-bench+0x18d6fc) (BuildId: 724e2958dfce8c8c5b51a12a902811a05da08c68)
    #3 silk::FiberMutex::lock(unsigned long*) contrib/silk/include/silk/fibers/mutex.h:60:9 (amber-storage-bench+0x10f7b4) (BuildId: 724e2958dfce8c8c5b51a12a902811a05da08c68)
    #4 std::unique_lock<silk::FiberMutex>::lock() /usr/lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/unique_lock.h:141:17 (amber-storage-bench+0x10f7b4)
    #5 std::unique_lock<silk::FiberMutex>::unique_lock(silk::FiberMutex&) /usr/lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/bits/unique_lock.h:71:2 (amber-storage-bench+0x10f7b4)
    #6 amber::LogWriter::flush() src/storage/log-writer.cpp:430:26 (amber-storage-bench+0x10f7b4)
    #7 amber::LogStoreImpl::runWriter(amber::LogWriter*) src/storage/log-store-worker.cpp:262:25 (amber-storage-bench+0x11f05c) (BuildId: 724e2958dfce8c8c5b51a12a902811a05da08c68)
    #8 amber::LogStoreImpl::writerFiberMain(amber::LogStoreImpl::WriterFiberParams*) src/storage/log-store.h:301:78 (amber-storage-bench+0x10cc2c) (BuildId: 724e2958dfce8c8c5b51a12a902811a05da08c68)
    #9 silk::Fiber::fiberContextMain(transfer_t) contrib/silk/src/fibers/fiber.cpp:469:21 (amber-storage-bench+0x17ffc4) (BuildId: 724e2958dfce8c8c5b51a12a902811a05da08c68)
    #10 make_fcontext contrib/silk/contrib/fcontext/asm/make_arm64_aapcs_elf_gas.S:94 (amber-storage-bench+0x1b1184) (BuildId: 724e2958dfce8c8c5b51a12a902811a05da08c68)

  Thread T430 (tid=40638, running) created by main thread at:
    #0 pthread_create <null> (amber-storage-bench+0x74dac) (BuildId: 724e2958dfce8c8c5b51a12a902811a05da08c68)
    #1 std::thread::_M_start_thread(std::unique_ptr<std::thread::_State, std::default_delete<std::thread::_State>>, void (*)()) <null> (libstdc++.so.6+0xe8b60) (BuildId: dd1ec2f8de311a1d2a43412b9ad99b3a5e8aa0fe)
    #2 benchmark::internal::(anonymous namespace)::ThreadRunnerDefault::RunThreads(std::function<void (int)> const&) contrib/benchmark/src/benchmark_runner.cc:202:18 (amber-storage-bench+0x15bdcc) (BuildId: 724e2958dfce8c8c5b51a12a902811a05da08c68)
    #3 benchmark::internal::BenchmarkRunner::DoNIterations() contrib/benchmark/src/benchmark_runner.cc:335:18 (amber-storage-bench+0x159870) (BuildId: 724e2958dfce8c8c5b51a12a902811a05da08c68)
    #4 benchmark::internal::BenchmarkRunner::DoOneRepetition() contrib/benchmark/src/benchmark_runner.cc:509:9 (amber-storage-bench+0x15b250) (BuildId: 724e2958dfce8c8c5b51a12a902811a05da08c68)
    #5 benchmark::internal::(anonymous namespace)::RunBenchmarks(std::vector<benchmark::internal::BenchmarkInstance, std::allocator<benchmark::internal::BenchmarkInstance>> const&, benchmark::BenchmarkReporter*, benchmark::BenchmarkReporter*) contrib/benchmark/src/benchmark.cc:484:14 (amber-storage-bench+0x122e10) (BuildId: 724e2958dfce8c8c5b51a12a902811a05da08c68)
    #6 benchmark::RunSpecifiedBenchmarks(benchmark::BenchmarkReporter*, benchmark::BenchmarkReporter*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>) contrib/benchmark/src/benchmark.cc:674:5 (amber-storage-bench+0x122e10)
    #7 benchmark::RunSpecifiedBenchmarks() contrib/benchmark/src/benchmark.cc:587:10 (amber-storage-bench+0x121f5c) (BuildId: 724e2958dfce8c8c5b51a12a902811a05da08c68)
    #8 main src/storage/benchmarks/main.cpp:14:5 (amber-storage-bench+0x106214) (BuildId: 724e2958dfce8c8c5b51a12a902811a05da08c68)

This looks like proxy-fiber was deleted and isFiberRunning uses a stale pointer. This does not happen with regular fibers because they are allocated from a memory pool.