sched/preempt: Fix up missed PREEMPT_NEED_RESCHED folding

With various drivers wanting to inject idle time; we get people
calling idle routines outside of the idle loop proper.

Therefore we need to be extra careful about not missing
TIF_NEED_RESCHED -> PREEMPT_NEED_RESCHED propagations.

While looking at this, I also realized there's a small window in the
existing idle loop where we can miss TIF_NEED_RESCHED; when it hits
right after the tif_need_resched() test at the end of the loop but
right before the need_resched() test at the start of the loop.

So move preempt_fold_need_resched() out of the loop where we're
guaranteed to have TIF_NEED_RESCHED set.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-x9jgh45oeayzajz2mjt0y7d6@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 15 insertions, 0 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a03875221663..ffccdad050b5 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2745,6 +2745,21 @@ static inline bool __must_check current_clr_polling_and_test(void)
 }
 #endif
 
+static inline void current_clr_polling(void)
+{
+	__current_clr_polling();
+
+	/*
+	 * Ensure we check TIF_NEED_RESCHED after we clear the polling bit.
+	 * Once the bit is cleared, we'll get IPIs with every new
+	 * TIF_NEED_RESCHED and the IPI handler, scheduler_ipi(), will also
+	 * fold.
+	 */
+	smp_mb(); /* paired with resched_task() */
+
+	preempt_fold_need_resched();
+}
+
 static __always_inline bool need_resched(void)
 {
 	return unlikely(tif_need_resched());