Which signal was delivered to process deadlocked in signal handler

Question

I have a core dump from a process that deadlocked after invoking a signal handler. How do I determine which signal was delivered and who sent it?

The GDB-generated backtrace for the the thread that received the signal follows. The signal handler was called in frame 15.

(gdb) bt
#0  0x00007fa9c204654b in sys_futex (w=0x7fa9c2263d80, value=2, loop=<value optimized out>) at ./src/base/linux_syscall_support.h:1789
#1  base::internal::SpinLockDelay (w=0x7fa9c2263d80, value=2, loop=<value optimized out>) at ./src/base/spinlock_linux-inl.h:87
#2  0x00007fa9c204774c in SpinLock::SlowLock (this=0x7fa9c2263d80) at src/base/spinlock.cc:132
#3  0x00007fa9c2037ee3 in Lock (this=0x7fa9c2263d80, start=0x7fa9bb3c04c8, end=0x7fa9bb3c04c0, N=3) at src/base/spinlock.h:75
#4  tcmalloc::CentralFreeList::RemoveRange (this=0x7fa9c2263d80, start=0x7fa9bb3c04c8, end=0x7fa9bb3c04c0, N=3) at src/central_freelist.cc:247
#5  0x00007fa9c203bae4 in tcmalloc::ThreadCache::FetchFromCentralCache (this=0x17efb40, cl=<value optimized out>, byte_size=32) at src/thread_cache.cc:162
#6  0x00007fa9c202b9cb in Allocate (size=<value optimized out>) at src/thread_cache.h:341
#7  do_malloc (size=<value optimized out>) at src/tcmalloc.cc:1068
#8  (anonymous namespace)::do_malloc_or_cpp_alloc (size=<value optimized out>) at src/tcmalloc.cc:1005
#9  0x00007fa9c204bfa8 in tc_realloc (old_ptr=0x0, new_size=32) at src/tcmalloc.cc:1517
#10 0x0000003a358c0f3b in ?? () from /usr/lib64/libstdc++.so.6
#11 0x0000003a358c2adf in ?? () from /usr/lib64/libstdc++.so.6
#12 0x0000003a358c2cae in __cxa_demangle () from /usr/lib64/libstdc++.so.6
#13 0x000000000085f6c7 in my_print_stacktrace ()
#14 0x00000000006a773a in handle_fatal_signal ()
#15 <signal handler called>
#16 tcmalloc::CentralFreeList::FetchFromSpans (this=0x7fa9c2263d80) at src/central_freelist.cc:298
#17 0x00007fa9c2037f88 in tcmalloc::CentralFreeList::RemoveRange (this=0x7fa9c2263d80, start=0x7fa9bb3c1468, end=0x7fa9bb3c1460, N=3) at src/central_freelist.cc:269
#18 0x00007fa9c203bae4 in tcmalloc::ThreadCache::FetchFromCentralCache (this=0x17efb40, cl=<value optimized out>, byte_size=32) at src/thread_cache.cc:162
...

For what it's worth, handle_fatal_signal() and my_print_stacktrace() are MySQL functions. The rest are from Google's tcmalloc.

Answer 1

I would try "frame 15" to move to the signal delivery frame, followed by "print $_siginfo.si_signo". See https://sourceware.org/gdb/onlinedocs/gdb/Signals.html

This works on Linux at least, which I presume from your backtrace that you are using. I'm not sure about other platforms.