(gdb) bt
#0  0x00007f811bb6d425 in __GI_raise (sig=<optimized out>) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
#1  0x00007f811bb70b8b in __GI_abort () at abort.c:91
#2  0x00007f811bbab39e in __libc_message (do_abort=2, fmt=0x7f811bcb5028 "*** glibc detected *** %s: %s: 0x%s ***\n") at ../sysdeps/unix/sysv/linux/libc_fatal.c:201
#3  0x00007f811bbb5b96 in malloc_printerr (action=3, str=0x7f811bcb5138 "double free or corruption (!prev)", ptr=<optimized out>) at malloc.c:5018
#4  0x0000000000447607 in internal_ao2_ref (user_data=0x1cb8308, delta=-1) at astobj2.c:286
#5  0x0000000000447502 in __ao2_ref (user_data=0x1cb8308, delta=-1) at astobj2.c:244
#6  0x00007f80f1f34a00 in unload_module () at chan_sip.c:31979
#7  0x00000000004ead43 in ast_unload_resource (resource_name=0x1cbc50e "chan_sip.so", force=AST_FORCE_SOFT) at loader.c:569
#8  0x000000000048c3ca in handle_unload (e=0x821e60 <cli_cli+3200>, cmd=-4, a=0x7fffc4458270) at cli.c:635
#9  0x0000000000492da1 in ast_cli_command_full (uid=-1, gid=-1, fd=1, s=0x11a8820 "module unload chan_sip.so ") at cli.c:2543
#10 0x000000000043d41a in consolehandler (s=0x11a8820 "module unload chan_sip.so ") at asterisk.c:1928
#11 0x000000000044430a in main (argc=2, argv=0x7fffc445a878) at asterisk.c:4093