xen/sched: fix race in RTDS scheduler

When a domain gets paused the unit runnable state can change to "not
runnable" without the scheduling lock being involved. This means that
a specific scheduler isn't involved in this change of runnable state.

In the RTDS scheduler this can result in an inconsistency in case a
unit is losing its "runnable" capability while the RTDS scheduler's
scheduling function is active. RTDS will remove the unit from the run
queue, but doesn't do so for the replenish queue, leading to hitting
an ASSERT() in replq_insert() later when the domain is unpaused again.

Fix that by removing the unit from the replenish queue as well in this
case.

Fixes: 7c7b407e7772 ("xen/sched: introduce unit_runnable_state()")
Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Dario Faggioli <dfaggioli@suse.com>
Release-acked-by: Henry Wang <Henry.Wang@arm.com>

diff --git a/xen/common/sched/rt.c b/xen/common/sched/rt.c
index d6de25531b3c7c88e8045d6c6415897a4df4e70f..960a8033e22253053ec907dff74ebf8863b5dfeb 100644 (file)
--- a/xen/common/sched/rt.c
+++ b/xen/common/sched/rt.c
@@ -1087,6 +1087,7 @@ rt_schedule(const struct scheduler *ops, struct sched_unit *currunit,
         else if ( !unit_runnable_state(snext->unit) )
         {
             q_remove(snext);
+            replq_remove(ops, snext);
             snext = rt_unit(sched_idle_unit(sched_cpu));
         }