TASK_DEAD is special in that the final schedule call from do_exit()
must be done with preemption disabled.
This leads to a violation of our new scheduling invariant which states
that the preempt count should be 2. Move the check for TASK_DEAD out
of the debug check and use it to decrement the preempt count (from 2
to 1).
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
kernel/sched/core.c | 19 +++++++++++++------
1 file changed, 13 insertions(+), 6 deletions(-)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2955,12 +2955,8 @@ static inline void schedule_debug(struct
#ifdef CONFIG_SCHED_STACK_END_CHECK
BUG_ON(unlikely(task_stack_end_corrupted(prev)));
#endif
- /*
- * Test if we are atomic. Since do_exit() needs to call into
- * schedule() atomically, we ignore that path. Otherwise whine
- * if we are scheduling when we should not.
- */
- if (unlikely(in_atomic_preempt_off() && prev->state != TASK_DEAD)) {
+
+ if (unlikely(in_atomic_preempt_off())) {
__schedule_bug(prev);
preempt_count_set(PREEMPT_DISABLED);
}
@@ -3061,6 +3057,17 @@ static void __sched __schedule(void)
rcu_note_context_switch();
prev = rq->curr;
+ /*
+ * do_exit() calls schedule() with preemption disabled as an exception;
+ * however we must fix that up, otherwise the next task will see an
+ * inconsistent preempt count.
+ *
+ * It also avoids the below schedule_debug() test from complaining
+ * about this.
+ */
+ if (unlikely(prev->state == TASK_DEAD))
+ preempt_enable_no_resched_notrace();
+
schedule_debug(prev);
if (sched_feat(HRTICK))
--
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