linux-kernel - [PATCH -rcu] rcu: Disable lazy if call

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Date:   Mon,  9 Jan 2023 22:17:56 +0000
From:   "Joel Fernandes (Google)" <joel@...lfernandes.org>
To:     linux-kernel@...r.kernel.org
Cc:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...nel.org>, rcu@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>, foo@....com
Subject: [PATCH -rcu] rcu: Disable lazy if call_rcu() called when GPs expedited

During suspend, we see failures to suspend 1 in 300-500 suspends.
Looking closer, it appears that we are queuing lazy callbacks even
though rcu_gp_is_expedited(). These delays appear to not be very welcome
by the suspend/resume code as evidenced by these occasional suspend
failures.

This commit therefore checks if rcu_gp_is_expedited() and ignores the
lazy hint if so.

Ignoring the lazy hint if rcu_gp_is_expedited() makes the 3000
suspend/resume cycles pass reliably on a 12th gen 12-core Intel CPU.

Fixes: 3cb278e73be5 ("rcu: Make call_rcu() lazy to save power")
Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
Paul, could we take this for 6.2 -rc cycle? Thanks.

 kernel/rcu/tree.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 63545d79da51..93eb03f8ed99 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2594,12 +2594,12 @@ static void check_cb_ovld(struct rcu_data *rdp)
 }
 
 static void
-__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy)
+__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in)
 {
 	static atomic_t doublefrees;
 	unsigned long flags;
 	struct rcu_data *rdp;
-	bool was_alldone;
+	bool was_alldone, lazy;
 
 	/* Misaligned rcu_head! */
 	WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
@@ -2622,6 +2622,7 @@ __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy)
 	kasan_record_aux_stack_noalloc(head);
 	local_irq_save(flags);
 	rdp = this_cpu_ptr(&rcu_data);
+	lazy = lazy_in && !rcu_gp_is_expedited();
 
 	/* Add the callback to our list. */
 	if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist))) {
-- 
2.39.0.314.g84b9a713c41-goog