Perfect, thanks Henning !. On Wednesday, September 18, 2019, 1:45:45 PM PDT, Henning Westerholt &lt;hw(a)skalatan.de&gt; wrote: Hello Rupesh, the lock mode was changed, you find the reasoning (and the linked commit) in this issue: https://github.com/kamailio/kamailio/issues/577 Cheers, Henning Am 18.09.19 um 22:05 schrieb Rupesh Kumar: Hi , Currently I am running kamailio 4.2 and now upgrading to kamailio 5.2 and was just going thru the changes. In the file modules/usrloc/udomain.c inside the function free_udomain( ) , it appears that we are not protecting via lock_ulslot and unlock_ulslot doing free. Could it cause some race condition ? May be its intentional but going thru the github history its there since day 1. I checked all branches in kamailio 4.x and we have the protection. In 4.x void free_udomain(udomain_t* _d) {     int i;          if (_d->table) {         for(i = 0; i < _d->size; i++) {             lock_ulslot(_d, i);             deinit_slot(_d->table + i);             unlock_ulslot(_d, i);         }         shm_free(_d->table);     }    shm_free(_d); } In 5.x void free_udomain(udomain_t* _d) {     int i;          if (_d->table) {         for(i = 0; i < _d->size; i++) {             deinit_slot(_d->table + i);         }         shm_free(_d->table);     }     shm_free(_d); } _______________________________________________ Kamailio (SER) - Users Mailing List sr-users(a)lists.kamailio.org https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users -- Kamailio Merchandising - https://skalatan.de/merchandising/ Kamailio services - https://skalatan.de/services Henning Westerholt - https://skalatan.de/blog/