base-hw scheduler: fix bug on removing head

The scheduler did not consider the consumed quota during a call to "update"
if the head that consumed the quota was removed from the scheduler. When this
occured, the internal round time did not advance as expected but remained at
its previous value untile the next call to "update" (without a removed head)
This commit introduces a new flag that is set only when the head gets removed
in order to detect and handle the situation correctly on the next call to
"update".

Ref #4151
Ref #4710

repos/base-hw/src/core/kernel/cpu_scheduler.cc

@@ -179,6 +179,13 @@ void Cpu_scheduler::update(time_t time)
 			_head_filled(r);
 
 		_consumed(duration);
+
+	} else if (_head_was_removed) {
+
+		_trim_consumption(duration);
+		_head_was_removed = false;
+		_head_yields = false;
+		_consumed(duration);
 	}
 
 	if (_claim_for_head())
@@ -258,8 +265,10 @@ void Cpu_scheduler::remove(Share &s)
 
 	if (s._ready) unready(s);
 
-	if (&s == _head)
+	if (&s == _head) {
 		_head = nullptr;
+		_head_was_removed = true;
+	}
 
 	if (!s._quota)
 		return;

repos/base-hw/src/core/kernel/cpu_scheduler.h

@@ -120,6 +120,7 @@ class Kernel::Cpu_scheduler
 		unsigned                _head_quota  = 0;
 		bool                    _head_claims = false;
 		bool                    _head_yields = false;
+		bool                    _head_was_removed = false;
 		unsigned const          _quota;
 		unsigned                _residual;
 		unsigned const          _fill;