safe_dump_to causes a deadlock if signal is received when throwing an exception

[tworonix]

Steps to reproduce

1. Install a timer using standard Posix timer_create and SIGEV_SIGNAL
2. Call safe_dump_to in the signal handler
3. Throw C++ exceptions in the main code

Actual behavior:
The process deadlocks and hangs forever.

When investigating this issue I found out that throwing an exception in C++ involves locking a mutex (see here for more details: https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2544r0.html )

Apparently both throwing the exception and collecting the stacktrace from the signal handler try to lock the same mutex. This leads to a deadlock, or possibly also other undefined behaviour.

Unfortunately this makes safe_dump_to not so safe to call from a signal handler, which I find very bad news. I wish there was a way to get it to work reliably. I was using quite old versions, but I don't think this was fixed in any newer releases of gcc or boost?

Platform details

boost-1.66, Linux Intel x64, gcc-8.2.1, library compiled with BOOST_STACKTRACE_USE_ADDR2LINE

Output of gdb after loading the coredump of the deadlocked process

#0  0x00007fc0bf18c4ed in __lll_lock_wait () from /lib64/libpthread.so.0
#1  0x00007fc0bf187dcb in _L_lock_883 () from /lib64/libpthread.so.0
#2  0x00007fc0bf187c98 in pthread_mutex_lock () from /lib64/libpthread.so.0
#3  0x00007fc0bdcfca2a in _Unwind_Find_FDE () from /lib64/libgcc_s.so.1
#4  0x00007fc0bdcf9d2c in ?? () from /lib64/libgcc_s.so.1
#5  0x00007fc0bdcfa6ed in ?? () from /lib64/libgcc_s.so.1
#6  0x00007fc0bdcfaf88 in _Unwind_Backtrace () from /lib64/libgcc_s.so.1
#7  0x00000000004ee1bd in boost::stacktrace::detail::this_thread_frames::collect (out_frames=0xfdf180 <Contoso::sDump>, max_frames_count=<optimized out>, skip=<optimized out>) at /opt/Contoso/boost/dts9/1.66.0/include/boost/stacktrace/detail/collect_unwind.ipp:59
#8  0x00000000004ee16c in boost::stacktrace::detail::this_thread_frames::safe_dump_to_impl (memory=0xfdf180 <Contoso::sDump>, size=<optimized out>, skip=<optimized out>) at /opt/Contoso/boost/dts9/1.66.0/include/boost/stacktrace/safe_dump_to.hpp:55
#9  0x00000000004ed492 in boost::stacktrace::safe_dump_to (memory=0x7fc0bdf00360, size=256) at /opt/Contoso/boost/dts9/1.66.0/include/boost/stacktrace/safe_dump_to.hpp:90
#10 Contoso::(anonymous namespace)::HandleTimerSignal (signum=<optimized out>) at /opt/contoso/build-dir/source/libs/stacktrace/stack_trace.cc:24
#11 <signal handler called>
#12 0x00007fc0bf188e1b in pthread_mutex_unlock () from /lib64/libpthread.so.0
#13 0x00007fc0bdcfca7a in _Unwind_Find_FDE () from /lib64/libgcc_s.so.1
#14 0x00007fc0bdcf9d2c in ?? () from /lib64/libgcc_s.so.1
#15 0x00007fc0bdcfabd3 in _Unwind_RaiseException () from /lib64/libgcc_s.so.1
#16 0x00007fc0be261986 in __cxa_throw () from /lib64/libstdc++.so.6
#17 0x0000000000508820 in Contoso::ThrowingFunction 

[itrofimow]

I was using quite old versions, but I don't think this was fixed in any newer releases of gcc or boost?

This doesn't really have much to do with boost, since the global lock in question comes from dl_iterate_phdr glibc function, which unwinders invoke when doing their stuff.

However, starting from glibc2.35 and gcc-12.3/llvm-16.0.0 this is no longer the case (at least it shouldn't be):
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71744#c32
https://reviews.llvm.org/D130668

[apolukhin]

Adding more clarification in #156

As @itrofimow noted, there's not much we can do in Boost.Stacktrace.

[apolukhin]

Many thanks to all the participants! The docs are updated, changes will be in Boost 1.85