[PATCH RT] fix IPI balancing for 4.14-rt

From: Clark Williams
Date: Tue Nov 21 2017 - 10:14:35 EST

From 8ea8311b75a40bdea03e7f8228a0578b6367e9d1 Mon Sep 17 00:00:00 2001
From: Clark Williams <williams@xxxxxxxxxx>
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@xxxxxxxxxx>
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);
- raw_spin_unlock(&rq->lock);
+ raw_spin_unlock_irq(&rq->lock);


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