From 125c578f0b5c33ba8ae5624f7ff2e6dfbc778be6 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Thu, 20 Dec 2012 18:28:26 +0100
Subject: [PATCH] block: Use cpu_chill() for retry loops

Retry loops on RT might loop forever when the modifying side was
preempted. Steven also observed a live lock when there was a
concurrent priority boosting going on.

Use cpu_chill() instead of cpu_relax() to let the system
make progress.

[bigeasy: After all those changes that occured over the years, this one hunk is
left and should not cause any starvation on -RT anymore]
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 block/blk-ioc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 9df50fb507ca..10244a1f8fee 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -9,6 +9,7 @@
 #include <linux/blkdev.h>
 #include <linux/slab.h>
 #include <linux/sched/task.h>
+#include <linux/delay.h>
 
 #include "blk.h"
 
@@ -116,7 +117,7 @@ static void ioc_release_fn(struct work_struct *work)
 			spin_unlock(&q->queue_lock);
 		} else {
 			spin_unlock_irqrestore(&ioc->lock, flags);
-			cpu_relax();
+			cpu_chill();
 			spin_lock_irqsave_nested(&ioc->lock, flags, 1);
 		}
 	}