On Thu 2020-10-01 13:13:07, Miroslav Benes wrote:
> On Wed, 30 Sep 2020, Evgenii Shatokhin wrote:
>
> > Hi,
> >
> > I wonder, can livepatch from the current mainline kernel patch the main
> > functions of kthreads, which are running or sleeping constantly? Are there any
> > best practices here?
>
> No. It is a "known" limitation, "" because we discussed it a couple of
> times (at least with Petr), but it is not documented :(
>
> I wonder if it is really an issue practically. I haven't met a case
> yet when we wanted to patch such thing. But yes, you're correct, it is not
> possible.
>
> > I mean, suppose we have a function which runs in a kthread (passed to
> > kthread_create()) and is organized like this:
> >
> > while (!kthread_should_stop()) {
> > ...
> > DEFINE_WAIT(_wait);
> > for (;;) {
> > prepare_to_wait(waitq, &_wait, TASK_INTERRUPTIBLE);
> > if (we_have_requests_to_process || kthread_should_stop())
> > break;
> > schedule();
> > }
> > finish_wait(waitq, &_wait);
> > ...
> > if (we_have_requests_to_process)
> > process_one_request();
> > ...
> > }
Crazy hack would be to patch only process_one_request() the following way:
1. Put the fixed main loop into the new process_one_request() function.
2. Put the original process_one_request() code into another function,
e.g. do_process_one_request_for_real() and call it from the
fixed loop.
Does it make any sense or should I provide some code?
Be aware that such patch could not get reverted because it would never
leave the new main loop.
Best Regards,
Petr
