linux/debian/patches-rt/0187-block-Use-cpu_chill-for-retry-loops.patch

From: Thomas Gleixner <tglx@linutronix.de>
Date: Thu, 20 Dec 2012 18:28:26 +0100
Subject: [PATCH 187/290] block: Use cpu_chill() for retry loops
Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=9cf22ca96dd1665b30609658a308c09ecb55c1c1

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.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 block/blk-ioc.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 01580f88fcb3..98d87e52ccdc 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"
 
@@ -118,7 +119,7 @@ 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);
 		}
 	}
@@ -202,7 +203,7 @@ void put_io_context_active(struct io_context *ioc)
 				spin_unlock(icq->q->queue_lock);
 			} else {
 				spin_unlock_irqrestore(&ioc->lock, flags);
-				cpu_relax();
+				cpu_chill();
 				goto retry;
 			}
 		}