[PATCH 5.10 64/70] rcu: Fix callbacks processing time limit retaining cond_resched()

[Greg Kroah-Hartman]

From: Frederic Weisbecker <frederic@xxxxxxxxxx>

commit 3e61e95e2d095e308616cba4ffb640f95a480e01 upstream.

The callbacks processing time limit makes sure we are not exceeding a
given amount of time executing the queue.

However its "continue" clause bypasses the cond_resched() call on
rcuc and NOCB kthreads, delaying it until we reach the limit, which can
be very long...

Make sure the scheduler has a higher priority than the time limit.

Reviewed-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Tested-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Tested-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Valentin Schneider <valentin.schneider@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
Cc: Uladzislau Rezki <urezki@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
[UR: backport to 5.10-stable + commit update]
Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 kernel/rcu/tree.c |   28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2490,10 +2490,22 @@ static void rcu_do_batch(struct rcu_data
 		 * Stop only if limit reached and CPU has something to do.
 		 * Note: The rcl structure counts down from zero.
 		 */
-		if (-rcl.len >= bl && !offloaded &&
-		    (need_resched() ||
-		     (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
-			break;
+		if (in_serving_softirq()) {
+			if (-rcl.len >= bl && (need_resched() ||
+					(!is_idle_task(current) && !rcu_is_callbacks_kthread())))
+				break;
+		} else {
+			local_bh_enable();
+			lockdep_assert_irqs_enabled();
+			cond_resched_tasks_rcu_qs();
+			lockdep_assert_irqs_enabled();
+			local_bh_disable();
+		}
+
+		/*
+		 * Make sure we don't spend too much time here and deprive other
+		 * softirq vectors of CPU cycles.
+		 */
 		if (unlikely(tlimit)) {
 			/* only call local_clock() every 32 callbacks */
 			if (likely((-rcl.len & 31) || local_clock() < tlimit))
@@ -2501,14 +2513,6 @@ static void rcu_do_batch(struct rcu_data
 			/* Exceeded the time limit, so leave. */
 			break;
 		}
-		if (offloaded) {
-			WARN_ON_ONCE(in_serving_softirq());
-			local_bh_enable();
-			lockdep_assert_irqs_enabled();
-			cond_resched_tasks_rcu_qs();
-			lockdep_assert_irqs_enabled();
-			local_bh_disable();
-		}
 	}
 
 	local_irq_save(flags);