From cafb748003e99b72641ba46b7139b33cc1dd264d Mon Sep 17 00:00:00 2001
Message-Id: <cafb748003e99b72641ba46b7139b33cc1dd264d.1599166691.git.zanussi@kernel.org>
In-Reply-To: <56457dc415803c8abc5acb513ada877a79596f05.1599166690.git.zanussi@kernel.org>
References: <56457dc415803c8abc5acb513ada877a79596f05.1599166690.git.zanussi@kernel.org>
From: Thomas Gleixner <tglx@linutronix.de>
Date: Thu, 20 Dec 2012 18:28:26 +0100
Subject: [PATCH 186/333] block: Use cpu_chill() for retry loops
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.142-rt63.tar.xz

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 4c810969c3e2..48089f5bcc11 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"
 
@@ -119,7 +120,7 @@ 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);
 		}
 	}
@@ -203,7 +204,7 @@ 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;
 			}
 		}
-- 
2.17.1

