Method SignalTrace

src/bthread/task_tracer.cpp:360–452

}

TaskTracer::Result TaskTracer::SignalTrace(pthread_t worker_tid) {
    // CAUTION:
    // https://github.com/gperftools/gperftools/wiki/gperftools'-stacktrace-capturing-methods-and-their-issues#libunwind
    // Generally, libunwind promises async-signal-safety for capturing backtraces.
    // But in practice, it is only partially async-signal-safe due to reliance on
    // dl_iterate_phdr API, which is used to enumerate all loaded ELF modules
    // (.so files and main executable binary). No libc offers dl_iterate_pdhr that
    // is async-signal-safe. In practice, the issue may happen if we take tracing
    // signal during an existing dl_iterate_phdr call (such as when the program
    // throws an exception) or during dlopen/dlclose-ing some .so module.
    // Deadlock call stack:
    // #0  __lll_lock_wait (futex=futex@entry=0x7f0d3d7f0990 <_rtld_global+2352>, private=0) at lowlevellock.c:52
    // #1  0x00007f0d3a73c131 in __GI___pthread_mutex_lock (mutex=0x7f0d3d7f0990 <_rtld_global+2352>) at ../nptl/pthread_mutex_lock.c:115
    // #2  0x00007f0d38eb0231 in __GI___dl_iterate_phdr (callback=callback@entry=0x7f0d38c456a0 <_ULx86_64_dwarf_callback>, data=data@entry=0x7f0d07defad0) at dl-iteratephdr.c:40
    // #3  0x00007f0d38c45d79 in _ULx86_64_dwarf_find_proc_info (as=0x7f0d38c4f340 <local_addr_space>, ip=ip@entry=139694791966897, pi=pi@entry=0x7f0d07df0498, need_unwind_info=need_unwind_info@entry=1, arg=0x7f0d07df0340) at dwarf/Gfind_proc_info-lsb.c:759
    // #4  0x00007f0d38c43260 in fetch_proc_info (c=c@entry=0x7f0d07df0340, ip=139694791966897) at dwarf/Gparser.c:461
    // #5  0x00007f0d38c44e46 in find_reg_state (sr=0x7f0d07defd10, c=0x7f0d07df0340) at dwarf/Gparser.c:925
    // #6  _ULx86_64_dwarf_step (c=c@entry=0x7f0d07df0340) at dwarf/Gparser.c:972
    // #7  0x00007f0d38c40c14 in _ULx86_64_step (cursor=cursor@entry=0x7f0d07df0340) at x86_64/Gstep.c:71
    // #8  0x00007f0d399ed8f6 in GetStackTraceWithContext_libunwind (result=<optimized out>, max_depth=63, skip_count=132054887, ucp=<optimized out>) at src/stacktrace_libunwind-inl.h:138
    // #9  0x00007f0d399ee083 in GetStackTraceWithContext (result=0x7f0d07df07b8, max_depth=63, skip_count=3, uc=0x7f0d07df0a40) at src/stacktrace.cc:305
    // #10 0x00007f0d399ea992 in CpuProfiler::prof_handler (signal_ucontext=<optimized out>, cpu_profiler=0x7f0d399f6600, sig=<optimized out>) at src/profiler.cc:359
    // #11 0x00007f0d399eb633 in ProfileHandler::SignalHandler (sig=27, sinfo=0x7f0d07df0b70, ucontext=0x7f0d07df0a40) at src/profile-handler.cc:530
    // #12 <signal handler called>
    // #13 0x00007f0d3a73c0b1 in __GI___pthread_mutex_lock (mutex=0x7f0d3d7f0990 <_rtld_global+2352>) at ../nptl/pthread_mutex_lock.c:115
    // #14 0x00007f0d38eb0231 in __GI___dl_iterate_phdr (callback=0x7f0d38f525f0, data=0x7f0d07df10c0) at dl-iteratephdr.c:40
    // #15 0x00007f0d38f536c1 in _Unwind_Find_FDE () from /lib/x86_64-linux-gnu/libgcc_s.so.1
    // #16 0x00007f0d38f4f868 in ?? () from /lib/x86_64-linux-gnu/libgcc_s.so.1
    // #17 0x00007f0d38f50a20 in ?? () from /lib/x86_64-linux-gnu/libgcc_s.so.1
    // #18 0x00007f0d38f50f99 in _Unwind_RaiseException () from /lib/x86_64-linux-gnu/libgcc_s.so.1
    // #19 0x00007f0d390088dc in __cxa_throw () from /lib/x86_64-linux-gnu/libstdc++.so.6
    // #20 0x00007f0d3b5b2245 in __cxxabiv1::__cxa_throw (thrownException=0x7f0d114ea8c0, type=0x7f0d3d6dd830 <typeinfo for rockset::GRPCError>, destructor=<optimized out>) at /src/folly/folly/experimental/exception_tracer/ExceptionTracerLib.cpp:107
    //
    // Therefore, use async-signal-safe absl::DefaultStackUnwinder instead of libunwind.

    if (pthread_equal(worker_tid, pthread_self())) {
        return Result::MakeErrorResult("Forbid to trace self");
    }

    // Each signal trace has an independent SignalSync to
    // prevent the previous SignalHandler from affecting the new SignalTrace.
    butil::intrusive_ptr<SignalSync> signal_sync(new SignalSync());
    if (!signal_sync->Init()) {
        return Result::MakeErrorResult("Fail to init SignalSync");
    }

    // Add reference for SignalHandler.
    signal_sync->AddRefManually();

    sigval value{};
    value.sival_ptr = signal_sync.get();
    size_t sigqueue_try = 0;
    while (pthread_sigqueue(worker_tid, _signal_num, value) != 0) {
        if (errno != EAGAIN || sigqueue_try++ >= 3) {
            // Remove reference for SignalHandler.
            signal_sync->RemoveRefManually();
            return Result::MakeErrorResult("Fail to pthread_sigqueue: %s", berror());
        }