Re: [PATCH][USBATM]: convert heavy init dances to kthread API

Duncan Sands wrote:
Hi,

The problem is that I couldn't find the maintainer for the code
in drivers/usb/atm/.

that would be me (though since I haven't used this modem in years I would
be more than happy to hand it off to someone else).

Besides, I don't have a proper hardware to test this.

I will try to find where I put my old modem and test your patch this weekend.

Oh, that would be great :)

@@ -1014,11 +1015,7 @@ static int usbatm_do_heavy_init(void *arg)
struct usbatm_data *instance = arg;
int ret;

- daemonize(instance->driver->driver_name);
allow_signal(SIGTERM);
- instance->thread_pid = current->pid;
-
- complete(&instance->thread_started);

One reason the completion existed to make sure that the thread was not
sent SIGTERM before the above call to allow_signal(SIGTERM). So I think
you have opened up a (tiny) race by deleting it.

Nope. See my answer below :)

static int usbatm_heavy_init(struct usbatm_data *instance)
{
- int ret = kernel_thread(usbatm_do_heavy_init, instance, CLONE_FS | CLONE_FILES);
-
- if (ret < 0) {
- usb_err(instance, "%s: failed to create kernel_thread (%d)!\n", __func__, ret);

Please don't delete this message.

- return ret;
- }
+ struct task_struct *t;

- wait_for_completion(&instance->thread_started);
+ t = kthread_create(usbatm_do_heavy_init, instance,
+ instance->driver->driver_name);
+ if (IS_ERR(t))
+ return PTR_ERR(t);

+ instance->thread = t;
+ wake_up_process(t);

Does the kthread API guarantee that the kthread is not running until you call

It does. That's why the race, you mentioned above is impossible.

wake_up_process? Because if not then what is to stop the kthread finishing before
this thread does "instance->thread = t", resulting in an attempt to send a signal
to a dead process later on in disconnect?

Otherwise it looks fine - thanks!

By the way, the right thing to do is (I think) to replace the thread with a workqueue
and have users of usbatm register a "shut_down" callback rather than using signals: the
disconnect method would call shut_down rathering than trying to kill the thread. That
way all this mucking around with pids etc wouldn't be needed. All users of usbatm would
need to be modified. I managed to convince myself once that they could all be fixed up
in a fairly simple manner thanks to a few tricks and a completion or two, but I don't
recall the details...

Well, that would be also great, since kill_proc will be gone - that's what
I'm trying to achieve.

Best wishes,

Duncan.


Thanks,
Pavel
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