linux-kernel - [PATCH RT] fix IPI balancing for 4.14-rt

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Message-ID: <20171121091425.7577dc02@tagon>
Date:   Tue, 21 Nov 2017 09:14:25 -0600
From:   Clark Williams <williams@...hat.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        John Kacur <jkacur@...hat.com>, Scott Wood <swood@...hat.com>,
        Mike Galbraith <efault@....de>
Subject: [PATCH RT] fix IPI balancing for 4.14-rt

From 8ea8311b75a40bdea03e7f8228a0578b6367e9d1 Mon Sep 17 00:00:00 2001
From: Clark Williams <williams@...hat.com>
Date: Mon, 20 Nov 2017 14:26:12 -0600
Subject: [PATCH] [rt] sched/rt: fix panic in double_lock_balance with
 simplified IPI RT balancing

I was testing 4.14-rt1 on a large system (cores == 96) and saw that
we were getting into an rt balancing storm, so I tried applying Steven's
patch (not upstream yet):

    sched/rt: Simplify the IPI rt balancing logic

Booting the resulting kernel yielded a panic in
double_lock_balance() due to irqs not being disabled.

This patch changes the calls to raw_spin_{lock,unlock} in the
function rto_push_irq_work_function, to be raw_spin_{lock,unlock}_irq.
Not sure if that's too heavy a hammer, but the resulting kernel boots
and runs and survives 12h runs of rteval. Once Steven's patch goes in 
upstream, we'll need something like this in RT.

Signed-off-by: Clark Williams <williams@...hat.com>
---
 kernel/sched/rt.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 57fb251dd8ce..a5cd0cea2f0f 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2008,9 +2008,9 @@ void rto_push_irq_work_func(struct irq_work *work)
 	 * When it gets updated, a check is made if a push is possible.
 	 */
 	if (has_pushable_tasks(rq)) {
-		raw_spin_lock(&rq->lock);
+		raw_spin_lock_irq(&rq->lock);
 		push_rt_tasks(rq);
-		raw_spin_unlock(&rq->lock);
+		raw_spin_unlock_irq(&rq->lock);
 	}
 
 	raw_spin_lock(&rq->rd->rto_lock);
-- 
2.14.3



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