Arch Linux

Description:

GDB hangs when debugging any multithreaded application. It was reproduced on at least two different ArchLinux machines with current updates installed.
Here's a backtrace of GDB when it happens (missing debug symbols, but maybe better than nothing):

(gdb) thread apply all bt

Thread 4 (Thread 0x7ff44423d700 (LWP 481)):
#0 0x00007ff446193b2f in pthread_cond_wait@@GLIBC_2.3.2 () from /usr/lib/libpthread.so.0
#1 0x00007ff445376457 in ?? () from /usr/lib/libgc.so.1
#2 0x00007ff44536c62f in ?? () from /usr/lib/libgc.so.1
#3 0x00007ff445374757 in ?? () from /usr/lib/libgc.so.1
#4 0x00007ff44618f124 in start_thread () from /usr/lib/libpthread.so.0
#5 0x00007ff4456ad4bd in clone () from /usr/lib/libc.so.6

Thread 3 (Thread 0x7ff443a3c700 (LWP 482)):
#0 0x00007ff446193b2f in pthread_cond_wait@@GLIBC_2.3.2 () from /usr/lib/libpthread.so.0
#1 0x00007ff445376457 in ?? () from /usr/lib/libgc.so.1
#2 0x00007ff44536c62f in ?? () from /usr/lib/libgc.so.1
#3 0x00007ff445374757 in ?? () from /usr/lib/libgc.so.1
#4 0x00007ff44618f124 in start_thread () from /usr/lib/libpthread.so.0
#5 0x00007ff4456ad4bd in clone () from /usr/lib/libc.so.6

Thread 2 (Thread 0x7ff44323b700 (LWP 483)):
#0 0x00007ff446193b2f in pthread_cond_wait@@GLIBC_2.3.2 () from /usr/lib/libpthread.so.0
#1 0x00007ff445376457 in ?? () from /usr/lib/libgc.so.1
#2 0x00007ff44536c62f in ?? () from /usr/lib/libgc.so.1
#3 0x00007ff445374757 in ?? () from /usr/lib/libgc.so.1
#4 0x00007ff44618f124 in start_thread () from /usr/lib/libpthread.so.0
#5 0x00007ff4456ad4bd in clone () from /usr/lib/libc.so.6

Thread 1 (Thread 0x7ff4474d4740 (LWP 479)):
#0 0x00007ff4455f8157 in sigsuspend () from /usr/lib/libc.so.6
#1 0x000000000049eae8 in ?? ()
#2 0x000000000049edae in ?? ()
#3 0x00000000004a060c in ?? ()
#4 0x000000000049f689 in iterate_over_lwps ()
#5 0x00000000004a1cd4 in ?? ()
#6 0x00000000004a8276 in ?? ()
#7 0x00000000005d394d in ?? ()
#8 0x00000000005dae63 in target_wait ()
#9 0x00000000005a70e9 in fetch_inferior_event ()
#10 0x00000000005bc77a in inferior_event_handler ()
#11 0x00000000005ba921 in ?? ()
#12 0x00000000005bacba in gdb_do_one_event ()
---Type <return> to continue, or q <return> to quit---
#13 0x00000000005baf2e in start_event_loop ()
#14 0x00000000005b4783 in ?? ()
#15 0x00000000005b1b2a in catch_errors ()
#16 0x00000000005b5766 in ?? ()
#17 0x00000000005b1b2a in catch_errors ()
#18 0x00000000005b5b0b in gdb_main ()
#19 0x000000000045adf5 in main ()

Additional info:
* package version(s)

$ uname -a
Linux milian-kdab2 3.15.8-1-ARCH #1 SMP PREEMPT Fri Aug 1 08:51:42 CEST 2014 x86_64 GNU/Linux

$ gcc --version
gcc (GCC) 4.9.1
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ gdb --version
GNU gdb (GDB) 7.8
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-unknown-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word".

* config and/or log files etc.


Steps to reproduce:

$ cat test.cpp
#include <thread>
#include <iostream>

using namespace std;

void doStuff()
{
cout << "hello world!\n";
}

int main()
{
thread t1(doStuff);
thread t2(doStuff);
thread t3(doStuff);
thread t4(doStuff);

t1.join();
t2.join();
t3.join();
t4.join();
return 0;
}

$ g++ -std=c++11 -lpthread test.cpp -o test
$ gdb ./test
GNU gdb (GDB) 7.8
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-unknown-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./test...(no debugging symbols found)...done.
(gdb) run
Starting program: /tmp/test
warning: Could not load shared library symbols for linux-vdso.so.1.
Do you need "set solib-search-path" or "set sysroot"?
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
[New Thread 0x7ffff6fe6700 (LWP 398)]
hello world!
[New Thread 0x7ffff67e5700 (LWP 399)]
[Thread 0x7ffff6fe6700 (LWP 398) exited]
hello world!

## it is stuck!
## I can't even interrupt it with CTRL+C:
^C
^C
^C
^C

^C^C^C^C^C^C

## output from a different terminal's ps aux | grep test
## milian 389 0.1 0.3 111340 28656 pts/5 Sl 15:43 0:00 gdb ./test
## milian 394 0.0 0.0 39352 1588 pts/5 tl+ 15:44 0:00 /tmp/test

## now I'll do a killall -s SIGCONT gdb from a different terminal

Program received signal SIGINT, Interrupt.
[Switching to Thread 0x7ffff67e5700 (LWP 399)]
0x00007ffff7bc4020 in __nptl_death_event () from /usr/lib/libpthread.so.0
(gdb)
(gdb) ## now I'll do a killall -s SIGCONT gdb from a different terminal
(gdb) ## huh? where am I now?
(gdb) bt
#0 0x00007ffff7bc4020 in __nptl_death_event () from /usr/lib/libpthread.so.0
#1 0x00007ffff7bc52c7 in start_thread () from /usr/lib/libpthread.so.0
#2 0x00007ffff70d04bd in clone () from /usr/lib/libc.so.6
(gdb) thread apply all bt
[New Thread 0x7ffff5fe4700 (LWP 400)]
(gdb) cont
Continuing.
[Thread 0x7ffff67e5700 (LWP 399) exited]
hello world!
## stuck again! sending SIGCONT one more time
[New Thread 0x7ffff57e3700 (LWP 451)]
hello world!
[Thread 0x7ffff5fe4700 (LWP 400) exited]
[Thread 0x7ffff57e3700 (LWP 451) exited]
[Inferior 1 (process 394) exited normally]
(gdb) ## stuck again! sending SIGCONT one more time
(gdb) bt
No stack.