From: Martin Schwidefsky Date: Mon, 28 Oct 2013 11:15:32 +0000 (+0100) Subject: s390/vtime: correct idle time calculation X-Git-Tag: firefly_0821_release~6453^2~239 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=d4f2a840c79ca283a453b9cd6329ccb530cb0f70;p=firefly-linux-kernel-4.4.55.git 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 Signed-off-by: Greg Kroah-Hartman --- diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c index 4f977d0d25c2..14647fe09d0c 100644 --- a/arch/s390/kernel/smp.c +++ b/arch/s390/kernel/smp.c @@ -933,7 +933,7 @@ 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); @@ -951,7 +951,7 @@ 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 3fb09359eda6..737d50caa4fe 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; }