[PATCH RT 4/5] block: Use cpu_chill() for retry loops

[Steven Rostedt]

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxx>
Cc: stable-rt@xxxxxxxxxxxxxxx
---
 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 fb95dd2..6b54201 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -8,6 +8,7 @@
 #include <linux/blkdev.h>
 #include <linux/bootmem.h>	/* for max_pfn/max_low_pfn */
 #include <linux/slab.h>
+#include <linux/delay.h>
 
 #include "blk.h"
 
@@ -110,7 +111,7 @@ 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);
 		}
 	}
@@ -188,7 +189,7 @@ retry:
 			spin_unlock(icq->q->queue_lock);
 		} else {
 			spin_unlock_irqrestore(&ioc->lock, flags);
-			cpu_relax();
+			cpu_chill();
 			goto retry;
 		}
 	}
-- 
1.7.10.4


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