Почему упал php-fpm

в логах последний строчки были такими:

Nov 25 11:50:23.477388 [NOTICE] fpm_children_bury(), line 217: child 14090 (pool default) exited with code 0 after 373.280193 seconds from start

Nov 25 11:50:23.477407 [NOTICE] fpm_children_bury(), line 217: child 14104 (pool default) exited with code 0 after 253.604035 seconds from start

Nov 25 11:50:23.498513 [NOTICE] fpm_got_signal(), line 48: received SIGCHLD

Nov 25 11:50:23.498576 [NOTICE] fpm_children_bury(), line 217: child 13770 (pool default) exited with code 0 after 3861.809194 seconds from start

Nov 25 11:50:23.498606 [NOTICE] fpm_children_bury(), line 217: child 13855 (pool default) exited with code 0 after 3013.701010 seconds from start

Nov 25 11:50:23.498627 [NOTICE] fpm_children_bury(), line 217: child 13942 (pool default) exited with code 0 after 1869.095148 seconds from start

Nov 25 11:50:23.505438 [NOTICE] fpm_got_signal(), line 48: received SIGCHLD

Nov 25 11:50:23.505499 [NOTICE] fpm_children_bury(), line 217: child 14088 (pool default) exited with code 0 after 408.017112 seconds from start

Nov 25 11:50:23.540983 [NOTICE] fpm_got_signal(), line 48: received SIGCHLD

Nov 25 11:50:23.541021 [NOTICE] fpm_children_bury(), line 217: child 14003 (pool default) exited with code 0 after 1293.697765 seconds from start

Nov 25 11:50:28.212485 [NOTICE] fpm_pctl_kill_all(), line 172: sending signal 15 SIGTERM to child 21345 (pool default)

Nov 25 11:50:28.212548 [NOTICE] fpm_pctl_kill_all(), line 181: 1 child is still alive

Nov 25 11:50:29.213476 [NOTICE] fpm_pctl_kill_all(), line 172: sending signal 9 SIGKILL to child 21345 (pool default)

Nov 25 11:50:29.213514 [NOTICE] fpm_pctl_kill_all(), line 181: 1 child is still alive

Nov 25 11:50:29.241134 [NOTICE] fpm_got_signal(), line 48: received SIGCHLD

Nov 25 11:50:29.241155 [WARNING] fpm_children_bury(), line 217: child 21345 (pool default) exited on signal 9 SIGKILL after 2569623.731520 seconds from start

Nov 25 11:50:29.241182 [NOTICE] fpm_pctl_exec(), line 95: reloading: execvp("/usr/bin/php-cgi", {"/usr/bin/php-cgi", "--fpm", "--fpm-config", "/etc/php-fpm.conf"})

php-cgi: event.c:268: event_base_free: Assertion `(((&base->eventqueue)->tqh_first) == ((void *)0))' failed.