nginx -t segfaults after upgrading lua-nginx-module to v0.10.14rc4

[fancy-rabbit]

CentOS7, kernel 3.10.0-862.11.6.el7.x86_64, nginx core 1.15.8, luajit 2.1-20190130
lua-nginx-module v0.10.14rc4, lua-resty-core v0.1.16rc4
expected behavior:
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful
but failed with:
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
Segmentation fault

minimal reproducible test case:

init_by_lua_block {
require "resty.core"
}
lua_shared_dict test 128k;

commenting out either init_by_lua_block or lua_shared_dict will succeed.

gdb result:

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7514ae0 in lj_vm_cpcall () from /lib64/libluajit-5.1.so.2
(gdb) bt
#0 0x00007ffff7514ae0 in lj_vm_cpcall () from /lib64/libluajit-5.1.so.2
#1 0x00007ffff756105d in lua_loadx () from /lib64/libluajit-5.1.so.2
#2 0x00007ffff75613dc in luaL_loadbufferx () from /lib64/libluajit-5.1.so.2
#3 0x0000555555710039 in ngx_http_lua_init_by_inline ()
#4 0x000055555570ce07 in ngx_http_lua_shared_memory_init ()
#5 0x000055555562d031 in ngx_init_cycle ()
#6 0x0000555555619eb8 in main ()

reverting commit 7c2b58e (#1377) resolved this issue.

[thibaultcha]

Thanks for the report, we will investigate as soon as possible.

[tokers]

@thibaultcha
When we have some lua_shared_dict directives, the execution of init_by_lua* will be postponed until the last shared memory is initialized, while after introducing 7c2b58e, the lmcf->lua isn't initialized yet at that moment. Maybe we can avoid initializing the shared memory in the signaller process.

[tokers]

Or just check the lmcf->lua in function ngx_http_lua_shared_memory_add, just like ngx_http_lua_init.

[thibaultcha]

I just merged @spacewander's proposed fix and released v0.10.14rc5 of this module with it. Considering this resolved, thank you for the testing and report!