(gdb) bt
#0  0x00007f4775cb44d4 in __lll_lock_wait () from /lib/libpthread.so.0
#1  0x00007f4775caff04 in _L_lock_547 () from /lib/libpthread.so.0
#2  0x00007f4775cafd66 in pthread_mutex_lock () from /lib/libpthread.so.0
#3  0x000000000040f656 in ?? ()
#4  0x000000000040c2f2 in ?? ()
#5  0x000000000040c3f7 in ?? ()
#6  0x0000000000403e23 in ?? ()
#7  0x00000000004043a5 in ?? ()
#8  0x00007f477596fa6d in __libc_start_main () from /lib/libc.so.6
#9  0x0000000000402d89 in ?? ()
#10 0x00007fff9f4f7cd8 in ?? ()
#11 0x000000000000001c in ?? ()
#12 0x0000000000000001 in ?? ()
#13 0x00007fff9f4f8947 in ?? ()
#14 0x0000000000000000 in ?? ()