On Fri, Oct 01, 2021 at 11:32:16AM +0100, Tvrtko Ursulin wrote:
On 01/10/2021 10:04, Tvrtko Ursulin wrote:
Hi Peter,
On 30/09/2021 19:33, Peter Zijlstra wrote:
On Thu, Sep 30, 2021 at 06:15:47PM +0100, Tvrtko Ursulin wrote:
void set_user_nice(struct task_struct *p, long nice) { bool queued, running; - int old_prio; + int old_prio, ret; struct rq_flags rf; struct rq *rq; @@ -6913,6 +6945,9 @@ void set_user_nice(struct task_struct *p, long nice) */ p->sched_class->prio_changed(rq, p, old_prio); + ret = atomic_notifier_call_chain(&user_nice_notifier_list, nice, p); + WARN_ON_ONCE(ret != NOTIFY_DONE);
out_unlock: task_rq_unlock(rq, p, &rf); }
No, we're not going to call out to exported, and potentially unbounded, functions under scheduler locks.
Agreed, that's another good point why it is even more hairy, as I have generally alluded in the cover letter.
Do you have any immediate thoughts on possible alternatives?
Like for instance if I did a queue_work from set_user_nice and then ran a notifier chain async from a worker? I haven't looked at yet what repercussion would that have in terms of having to cancel the pending workers when tasks exit. I can try and prototype that and see how it would look.
Hm or I simply move calling the notifier chain to after task_rq_unlock? That would leave it run under the tasklist lock so probably still quite bad.
Hmm? That's for normalize_rt_tasks() only, right? Just don't have it call the notifier in that special case (that's a magic sysrq thing anyway).