s390/vtime: correct idle time calculation

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@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index 1a4313a1b60f76e20ac50ff31b5c0d2e0bf95492..93439cd044066d2b28bb430f62d439f619ddc6cf 100644 (file)
--- 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 abcfab55f99b37e5d4f79903be716e67896d5c79..bb06a76040bf59c75b99418cab8e6f14720a86c5 100644 (file)
--- a/arch/s390/kernel/vtime.c
+++ b/arch/s390/kernel/vtime.c
@@ -191,7 +191,7 @@ 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;
 }