Crashes in timer code when ngx_log_debug is on

[lev.apcera.com@…]

There is now code that looks like
​https://github.com/nginx/nginx/blob/6454225872c058c2705fc1e207ce4bb503b2e12a/src/event/ngx_event_timer.h#L69-L71

ngx_log_debug3(NGX_LOG_DEBUG_EVENT, ...ngx_event_ident(ev->data), ...);

ngx_event_ident takes an ngx_connection*, we use timers with custom data pointers in our code, not tied to a specific connection, so the above line crashes in debug mode.

There are several other instances of this, easily greppable

[Valentin V. Bartenev]

This ticket reminds me an old joke: “The patient says "Doctor, it hurts when I do this." "Then don't do that!"”

[Maxim Dounin]

The ev->data field is expected to contain ngx_connection_t or a structure compatible with it for ngx_event_data(). For example, ngx_open_file_cache_event_t does the following:

typedef struct {

    /* ngx_connection_t stub to allow use c->fd as event ident */
    void                    *data;
    ngx_event_t             *read;
    ngx_event_t             *write;
    ngx_fd_t                 fd;

    ...
} ngx_open_file_cache_event_t;

and here is a quote from resolver code:

struct ngx_resolver_s {
    /* has to be pointer because of "incomplete type" */
    ngx_event_t              *event;
    void                     *dummy;
    ngx_log_t                *log;

    /* event ident must be after 3 pointers as in ngx_connection_t */
    ngx_int_t                 ident;

    ...

While this may be non-intuitive and not convenient in some cases, this is how it works. If your module does not provide appropriate ev->data, an obvious solution would be to fix the module.

[lev.apcera.com@…]

Thanks for the explanation!