Race when both aio threads and background subrequests are used

[guo.bojun@…]

When the specific configurations are set(e.g. aio threads + proxy_cache_background_update on), multiple threads can operate on the same request connection structure and ​https://hg.nginx.org/nginx/file/tip/src/event/ngx_event_openssl.c#l3361
can cause ngx_ssl_recv() call from another thread to access a NULL c->ssl pointer.

[Maxim Dounin]

Could you please provide more details? A test case which demonstrates the problem would be helpful, as well as "nginx -V".

Note that threaded operations are not expected to access connection structures, but rather implement simple primitives, such as reading from a file, writing to a file, or sending a file with the sendfile() syscall to a specific socket. As such, it is certainly not possible that multiple threads can operate on the same connection structure. Further, the ngx_ssl_shutdown() function you've linked is not expected to be called unless all background subrequests have been completed. If you observe issues with a particular configuration, there should be another explanation.