linux-kernel - [PATCH 3.11 240/272] s390/vtime: correct idle time calculation

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Date:	Fri,  6 Dec 2013 12:58:49 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.11 240/272] s390/vtime: correct idle time calculation

3.11.10.1 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Martin Schwidefsky <schwidefsky@...ibm.com>

commit 4560e7c3317c7a2b370e36dadd3a3bac2ed70818 upstream.

Use the ACCESS_ONCE macro for both accesses to idle->sequence in the
loops to calculate the idle time. If only one access uses the macro,
the compiler is free to cache the value for the second access which
can cause endless loops.

Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 arch/s390/kernel/smp.c   | 4 ++--
 arch/s390/kernel/vtime.c | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index d386c4e..dcd2ac1 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -929,7 +929,7 @@ static ssize_t show_idle_count(struct device *dev,
 		idle_count = ACCESS_ONCE(idle->idle_count);
 		if (ACCESS_ONCE(idle->clock_idle_enter))
 			idle_count++;
-	} while ((sequence & 1) || (idle->sequence != sequence));
+	} while ((sequence & 1) || (ACCESS_ONCE(idle->sequence) != sequence));
 	return sprintf(buf, "%llu\n", idle_count);
 }
 static DEVICE_ATTR(idle_count, 0444, show_idle_count, NULL);
@@ -947,7 +947,7 @@ static ssize_t show_idle_time(struct device *dev,
 		idle_time = ACCESS_ONCE(idle->idle_time);
 		idle_enter = ACCESS_ONCE(idle->clock_idle_enter);
 		idle_exit = ACCESS_ONCE(idle->clock_idle_exit);
-	} while ((sequence & 1) || (idle->sequence != sequence));
+	} while ((sequence & 1) || (ACCESS_ONCE(idle->sequence) != sequence));
 	idle_time += idle_enter ? ((idle_exit ? : now) - idle_enter) : 0;
 	return sprintf(buf, "%llu\n", idle_time >> 12);
 }
diff --git a/arch/s390/kernel/vtime.c b/arch/s390/kernel/vtime.c
index 9b9c1b7..6d1f7bb 100644
--- a/arch/s390/kernel/vtime.c
+++ b/arch/s390/kernel/vtime.c
@@ -190,7 +190,7 @@ cputime64_t s390_get_idle_time(int cpu)
 		sequence = ACCESS_ONCE(idle->sequence);
 		idle_enter = ACCESS_ONCE(idle->clock_idle_enter);
 		idle_exit = ACCESS_ONCE(idle->clock_idle_exit);
-	} while ((sequence & 1) || (idle->sequence != sequence));
+	} while ((sequence & 1) || (ACCESS_ONCE(idle->sequence) != sequence));
 	return idle_enter ? ((idle_exit ?: now) - idle_enter) : 0;
 }
 
-- 
1.8.3.2

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