[systemd-devel] possible message leak in bus->wqueue ?

[cee1]

2015-08-07 17:18 GMT+08:00 eshark <eshark77 at 163.com>:
> Hi, all
>       If  some message went into bus->wqueue, and  failed to run
> ioctl(KDBUS_CMD_SEND) and returned  r < 0,
> I found that this message will remain in the bus->wqueue.   If  the peer is
> killed for some reason, this message will fail to be sent and remain in the
> wqueu for ever.
>
> Because in  dispatch_wqueue() ,  when bus_write_message() return r <0,
> dispatch_wqueue() will simply return this  "r " into the caller.
> And the wqueue is invisible to user application, so user application also
> cannot   remove this message to handle this error case.
>
>  I wonder whether this is a problem, and if yes,  should we remove this
> message  in dispatch_wqueue() when  r < 0 ?

I've the same question.

E.g.

dispatch_wqueue()
    bus_write_message()
        bus_kernel_write_message()

"""
r = ioctl(bus->output_fd, KDBUS_CMD_SEND, &cmd);
if (r < 0) {
    ...
    else if (errno == ENXIO || errno == ESRCH) {
                        ...
                        if (m->header->type == SD_BUS_MESSAGE_METHOD_CALL)
                                sd_bus_error_setf(&error,
SD_BUS_ERROR_SERVICE_UNKNOWN, "Destination %s not known",
m->destination);
                        else {
                                log_debug("Could not deliver message
to %s as destination is not known. Ignoring.", m->destination);
                                return 0;
                        }
}
"""

If A __returns__ a result to B, but B has already died (After sending
a "method call" message):

1. It will return ENXIO or ESRCH, right?
2. dispatch_wqueue(), bus_write_message()  and
bus_kernel_write_message() returns 0
3. Next time dispatch_wqueue() called, it will retry, but never
succeed - so, deadlocked?



-- 
Regards,

- cee1