Messages in this thread | | | Date | Thu, 31 Mar 2005 16:27:58 -0800 | From | Andrew Morton <> | Subject | Re: [1/1] CBUS: new very fast (for insert operations) message bus based on kenel connector. |
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Evgeniy Polyakov <johnpol@2ka.mipt.ru> wrote: > > I'm pleased to annouce CBUS - ultra fast (for insert operations) > message bus.
> +static int cbus_enqueue(struct cbus_event_container *c, struct cn_msg *msg) > +{ > + int err; > + struct cbus_event *event; > + unsigned long flags; > + > + event = kmalloc(sizeof(*event) + msg->len, GFP_ATOMIC);
Using GFP_ATOMIC is a bit lame. It would be better to require the caller to pass in the gfp_flags. Or simply require that all callers not hold locks and use GFP_KERNEL.
> +static int cbus_process(struct cbus_event_container *c, int all) > +{ > + struct cbus_event *event; > + int len, i, num; > + > + if (list_empty(&c->event_list)) > + return 0; > + > + if (all) > + len = c->qlen; > + else > + len = 1; > + > + num = 0; > + for (i=0; i<len; ++i) { > + event = cbus_dequeue(c); > + if (!event) > + continue; > + > + cn_netlink_send(&event->msg, 0); > + num++; > + > + kfree(event); > + } > + > + return num; > +}
It might be cleaner to pass in an item count rather than a boolean `all' here. Then again, it seems racy.
The initial list_empty() call could fail to detect new events due to lack of locking and memory barriers.
We conventionally code for loops as
for (i = 0; i < len; i++)
> +static int cbus_event_thread(void *data) > +{ > + int i, non_empty = 0, empty = 0; > + struct cbus_event_container *c; > + > + daemonize(cbus_name); > + allow_signal(SIGTERM); > + set_user_nice(current, 19);
Please use the kthread api for managing this thread.
Is a new kernel thread needed?
> + while (!cbus_need_exit) { > + if (empty || non_empty == 0 || non_empty > 10) { > + interruptible_sleep_on_timeout(&cbus_wait_queue, 10);
interruptible_sleep_on_timeout() is heavily deprecated and is racy without external locking (it pretty much has to be the BKL). Use wait_event_timeout().
> +int __devinit cbus_init(void) > +{ > + int i, err = 0; > + struct cbus_event_container *c; > + > + for_each_cpu(i) { > + c = &per_cpu(cbus_event_list, i); > + cbus_init_event_container(c); > + } > + > + init_completion(&cbus_thread_exited); > + > + cbus_pid = kernel_thread(cbus_event_thread, NULL, CLONE_FS | CLONE_FILES);
Using the kthread API would clean this up.
> + if (IS_ERR((void *)cbus_pid)) {
The weird cast here might not even work at all on 64-bit architectures. It depends if they sign extend ints when casting them to pointers. I guess they do. If cbus_pid is indeed an s32.
Much better to do
if (cbus_pid < 0)
> +void __devexit cbus_fini(void) > +{ > + int i; > + struct cbus_event_container *c; > + > + cbus_need_exit = 1; > + kill_proc(cbus_pid, SIGTERM, 0); > + wait_for_completion(&cbus_thread_exited); > + > + for_each_cpu(i) { > + c = &per_cpu(cbus_event_list, i); > + cbus_fini_event_container(c); > + } > +}
I think this is racy. What stops new events from being queued while this function is in progress?
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