### Description

When Kamailio child core generated, then Kamailio goes to shutdown. I observed a case when the Kamailio process shutdown process a deadlocked and not able to shutdown for a long time.

#### Debugging Data ``` (gdb) bt #0 0x0000ffff8645b648 in sched_yield () from /lib64/libc.so.6 #1 0x0000000000527820 in timer_del_safe (tl=0xffff841969f8) at core/timer.c:718 #2 0x0000ffff80121630 in unlink_timers (t=0xffff84196738) at timer.h:363 #3 0x0000ffff80122488 in free_cell_helper (dead_cell=0xffff84196738, silent=1, fname=0xffff8022be70 "h_table.c", fline=466) at h_table.c:150 #4 0x0000ffff80124bac in free_hash_table () at h_table.c:466 #5 0x0000ffff801da5c0 in tm_shutdown () at t_funcs.c:88 #6 0x00000000005c8e08 in destroy_modules () at core/sr_module.c:830 #7 0x000000000041df3c in cleanup (show_status=1) at main.c:575 #8 0x000000000041ffd4 in shutdown_children (sig=15, show_status=1) at main.c:718 #9 0x0000000000423a90 in handle_sigs () at main.c:816 #10 0x0000000000433018 in main_loop () at main.c:1903 #11 0x000000000043de90 in main (argc=11, argv=0xfffffac1fb18) at main.c:3053 (gdb) f 1 #1 0x0000000000527820 in timer_del_safe (tl=0xffff841969f8) at core/timer.c:718 718 sched_yield(); /* wait for it to complete */ (gdb) list 713 tl->add_line, tl->del_calls, tl->del_func, 714 tl->del_file, tl->del_line, tl->init, tl->expires_no); 715 #endif 716 return -2; /* do nothing */ 717 } 718 sched_yield(); /* wait for it to complete */ 719 goto again; 720 } 721 if ((tl->next!=0)&&(tl->prev!=0)){ 722 _timer_rm_list(tl); /* detach */ (gdb) bt full #0 0x0000ffff8645b648 in sched_yield () from /lib64/libc.so.6 No symbol table info available. #1 0x0000000000527820 in timer_del_safe (tl=0xffff841969f8) at core/timer.c:718 ret = -1 __func__ = "timer_del_safe" #2 0x0000ffff80121630 in unlink_timers (t=0xffff84196738) at timer.h:363 i = 0 #3 0x0000ffff80122488 in free_cell_helper (dead_cell=0xffff84196738, silent=1, fname=0xffff8022be70 "h_table.c", fline=466) at h_table.c:150 b = 0x0 i = 65535 rpl = 0x0 tt = 0x0 foo = 0xffff80089b00 <__func__.11765> cbs = 0x0 cbs_tmp = 0xffff83817f88 __func__ = "free_cell_helper" #4 0x0000ffff80124bac in free_hash_table () at h_table.c:466 p_cell = 0xffff84196738 tmp_cell = 0xffff80606630 i = 33128 __func__ = "free_hash_table" #5 0x0000ffff801da5c0 in tm_shutdown () at t_funcs.c:88 __func__ = "tm_shutdown" #6 0x00000000005c8e08 in destroy_modules () at core/sr_module.c:830 t = 0xffff84c44808 foo = 0xffff84c44038 __func__ = "destroy_modules" #7 0x000000000041df3c in cleanup (show_status=1) at main.c:575 memlog = 435649383 __func__ = "cleanup" #8 0x000000000041ffd4 in shutdown_children (sig=15, show_status=1) at main.c:718 __func__ = "shutdown_children" #9 0x0000000000423a90 in handle_sigs () at main.c:816 chld = 0 chld_status = 139 any_chld_stopped = 1 memlog = 4403228 __func__ = "handle_sigs" #10 0x0000000000433018 in main_loop () at main.c:1903 i = 8 pid = 175104 si = 0x0 si_desc = "udp receiver child=7 sock=[2600:1f18:578:5703::c6]:5080\000\220\352Ą\377\377\000\000@\365\301\372\377\377\000\000\360\004)\205\377\377\000\000`\365\301\372\377\377\000\000p\365\301\372\377\377\000\000p\365\301\372\377\377\000\000@\365\301\372\377\377\000\000\320\377\377\377\200\377\377\377\000l\377\362g{\367\031" nrprocs = 8 woneinit = 1 __func__ = "main_loop" #11 0x000000000043de90 in main (argc=11, argv=0xfffffac1fb18) at main.c:3053 cfg_stream = 0x177f02d0 c = -1 r = 0 tmp = 0xfffffac1fee1 "" tmp_len = 65535 port = 1 proto = 0 ahost = 0x0 aport = 0 options = 0x8ae128 ":f:cm:M:dVIhEeb:l:L:n:vKrRDTN:W:w:t:u:g:P:G:SQ:O:a:A:x:X:Y:" ret = -1 seed = 4190370820 rfd = 4 debug_save = 0 debug_flag = 0 dont_fork_cnt = 2 n_lst = 0x0 p = 0xffff863c0da8 <__libc_start_main+168> "" st = {st_dev = 25, st_ino = 18103, st_mode = 16832, st_nlink = 2, st_uid = 991, st_gid = 986, st_rdev = 0, __pad1 = 0, st_size = 60, st_blksize = 65536, __pad2 = 0, st_blocks = 0, st_atim = {tv_sec = 1624774599, tv_nsec = 29999981}, st_mtim = {tv_sec = 1625138047, tv_nsec = 607511242}, st_ctim = {tv_sec = 1625138047, tv_nsec = 607511242}, __glibc_reserved = {0, 0}} tbuf = "\000\000\000\000\000\000\000\000\000\000n\206\377\377\000\000\000\000\000\000\000\000\000\000\330\375q\206\377\377", '\000' <repeats 58 times>, "x\376q\206\377\377\000\000h\376q\206\377\377\000\000\b\376q\206\377\377\000\000(\376q\206\377\377\000\000\070\376q\206\377\377\000\000\250\376q\206\377\377\000\000\270\376q\206\377\377\000\000\310\376q\206\377\377\000\000H\376q\206\377\377\000\000X\376q\206\377\377", '\000' <repeats 18 times>, "\330\375q\206\377\377", '\000' <repeats 42 times>... option_index = 12 long_options = {{name = 0x8b04e8 "help", has_arg = 0, flag = 0x0, val = 104}, {name = 0x8ab520 "version", has_arg = 0, flag = 0x0, val = 118}, {name = 0x8b04f0 "alias", has_arg = 1, flag = 0x0, val = 1024}, {name = 0x8b04f8 "subst", has_arg = 1, flag = 0x0, val = 1025}, {name = 0x8b0500 "substdef", has_arg = 1, flag = 0x0, val = 1026}, {name = 0x8b0510 "substdefs", has_arg = 1, flag = 0x0, val = 1027}, {name = 0x8b0520 "server-id", has_arg = 1, flag = 0x0, val = 1028}, {name = 0x8b0530 "loadmodule", has_arg = 1, flag = 0x0, val = 1029}, {name = 0x8b0540 "modparam", has_arg = 1, flag = 0x0, val = 1030}, {name = 0x8b0550 "log-engine", has_arg = 1, flag = 0x0, val = 1031}, {name = 0x8b0560 "debug", has_arg = 1, flag = 0x0, val = 1032}, {name = 0x8b0568 "cfg-print", has_arg = 0, flag = 0x0, val = 1033}, {name = 0x8b0578 "atexit", has_arg = 1, flag = 0x0, val = 1034}, {name = 0x0, has_arg = 0, flag = 0x0, val = 0}} __func__ = "main" (gdb) info locals ret = -1 __func__ = "timer_del_safe" ```

### Additional Information

* **Kamailio Version** - output of `kamailio -v`

``` [root@bcf-e-3 ~]# kamailio -v version: kamailio 5.6.0-dev0 (aarch64/linux) f03900 flags: USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MMAP, PKG_MALLOC, Q_MALLOC, F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY, USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT-NOSMP, USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLOCKLIST, HAVE_RESOLV_RES, TLS_PTHREAD_MUTEX_SHARED ADAPTIVE_WAIT_LOOPS 1024, MAX_RECV_BUFFER_SIZE 262144, MAX_URI_SIZE 1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 8MB poll method support: poll, epoll_lt, epoll_et, sigio_rt, select. id: f03900 compiled on 17:17:36 Jun 26 2021 with gcc 8.4.1 ``` Used master branch with customization.

* **Operating System**:

``` [root@bcf-e-3 ~]# uname -a Linux bcf-e-3.la.cal911.net 4.18.0-305.3.1.el8.aarch64 #1 SMP Tue Jun 1 16:22:50 UTC 2021 aarch64 aarch64 aarch64 GNU/Linux [root@bcf-e-3 ~]# cat /etc/os-release NAME="CentOS Linux" VERSION="8" ID="centos" ID_LIKE="rhel fedora" VERSION_ID="8" PLATFORM_ID="platform:el8" PRETTY_NAME="CentOS Linux 8" ANSI_COLOR="0;31" CPE_NAME="cpe:/o:centos:centos:8" HOME_URL="https://centos.org/" BUG_REPORT_URL="https://bugs.centos.org/" CENTOS_MANTISBT_PROJECT="CentOS-8" CENTOS_MANTISBT_PROJECT_VERSION="8" ```