Messages in this thread | | | Date | Mon, 4 Jun 2018 13:03:25 -0500 | From | Josh Poimboeuf <> | Subject | Re: [PATCH 1/2] livepatch: Send a fake signal periodically |
| |
On Mon, Jun 04, 2018 at 04:16:35PM +0200, Miroslav Benes wrote: > An administrator may send a fake signal to all remaining blocking tasks > of a running transition by writing to > /sys/kernel/livepatch/<patch>/signal attribute. Let's do it > automatically after 10 seconds. The timeout is chosen deliberately. It > gives the tasks enough time to transition themselves. > > Theoretically, sending it once should be more than enough. Better be safe > than sorry, so send it periodically.
This is the part I don't understand. Why do it periodically?
Instead, might it make sense to just send the signals once, and if that doesn't work, reverse the transition? Then we could make patching a synchronous operation. But then, it might be remotely possible that the reverse operation also stalls (e.g., on a kthread). So, maybe it's best to just leave all these controls in the hands of the user.
All that said, a few code review comments:
- AFAICT, it does an 8 second delay instead of a 10 second delay, because
a) try_complete_transition() is first called before there's any delay;
b) the preincrement operator used on signals_cnt.
- I think 15 seconds might be a better default. I've seen longer patching delays on a system with 100+ CPUs.
- If a kthread or idle task is sleeping on a patched function, the pr_notice("signaling remaining tasks\n") will be repeated continously.
- It might be cleaner to do it from the delayed work function (klp_transition_work_fn).
-- Josh
| |