On Mon, Jan 11, 2021 at 01:25:59PM +0100, Peter Zijlstra wrote:
On Sat, Jan 09, 2021 at 03:05:34AM +0100, Frederic Weisbecker wrote:
The idle loop has several need_resched() checks that make sure we don't miss a rescheduling request. This means that any wake up performed on the local runqueue after the last generic need_resched() check is going to have its rescheduling silently ignored. This has happened in the past with rcu kthreads awaken from rcu_idle_enter() for example.
Perform sanity checks to report these situations.
I really don't like this..
- it's too specific to the actual reschedule condition, any wakeup this late is dodgy, not only those that happen to cause a local reschedule.
Right.
we can already test this with unwind and checking against __cpuidle
moving all of __cpuidle into noinstr would also cover this. And we're going to have to do that anyway.
Ok then, I'll wait for that instead.
+void noinstr sched_resched_local_assert_allowed(void) +{
- if (this_rq()->resched_local_allow)
return;
- /*
* Idle interrupts break the CPU from its pause and* rescheduling happens on idle loop exit.*/- if (in_hardirq())
return;- /*
* What applies to hardirq also applies to softirq as* we assume they execute on hardirq tail. Ksoftirqd* shouldn't have resched_local_allow == 0.* We also assume that no local_bh_enable() call may* execute softirqs inline on fragile idle/entry* path...*/- if (in_serving_softirq())
return;- WARN_ONCE(1, "Late current task rescheduling may be lost\n");
That seems like it wants to be:
WARN_ONCE(in_task(), "...");
Right! But I guess I'll drop that patch now.
Thanks.