Re: [PATCH 6/6] sched: Change task_struct::state

Peter Zijlstra
2021-06-02T14:21:32Z

On Wed, Jun 02, 2021 at 10:06:58AM -0400, Mathieu Desnoyers wrote:
> ----- On Jun 2, 2021, at 9:12 AM, Peter Zijlstra peterz@infradead.org wrote:

> > @@ -134,14 +134,14 @@ struct task_group;
> > do { \
> > WARN_ON_ONCE(is_special_task_state(state_value));\
> > current->task_state_change = _THIS_IP_; \
> > - current->state = (state_value); \
> > + WRITE_ONCE(current->__state, (state_value)); \
> > } while (0)
>
> Why not introduce set_task_state(p) and get_task_state(p) rather than sprinkle
> READ_ONCE() and WRITE_ONCE() all over the kernel ?

set_task_state() is fundamentally unsound, there's very few sites that
_set_ state on anything other than current, and those sites are super
tricky, eg. ptrace.

Having get_task_state() would seem to suggest it's actually a sane thing
to do, it's not really. Inspecting remote state is full of races, and
some of that really wants cleaning up, but that's for another day.