From: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
commit 3d7efa4edd07be5c5c3ffa95ba63e97e070e1f3f upstream.
The idle time reported in /proc/stat sometimes incorrectly contains
huge values on s390. This is caused by a bug in arch_cpu_idle_time().
The kernel tries to figure out when a different cpu entered idle by
accessing its per-cpu data structure. There is an ordering problem: if
the remote cpu has an idle_enter value which is not zero, and an
idle_exit value which is zero, it is assumed it is idle since
"now". The "now" timestamp however is taken before the idle_enter
value is read.
Which in turn means that "now" can be smaller than idle_enter of the
remote cpu. Unconditionally subtracting idle_enter from "now" can thus
lead to a negative value (aka large unsigned value).
Fix this by moving the get_tod_clock() invocation out of the
loop. While at it also make the code a bit more readable.
A similar bug also exists for show_idle_time(). Fix this is as well.
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/s390/kernel/idle.c | 29 ++++++++++++++++++++++-------
1 file changed, 22 insertions(+), 7 deletions(-)
--- a/arch/s390/kernel/idle.c
+++ b/arch/s390/kernel/idle.c
@@ -69,18 +69,26 @@ DEVICE_ATTR(idle_count, 0444, show_idle_
static ssize_t show_idle_time(struct device *dev,
struct device_attribute *attr, char *buf)
{
+ unsigned long long now, idle_time, idle_enter, idle_exit, in_idle;
struct s390_idle_data *idle = &per_cpu(s390_idle, dev->id);
- unsigned long long now, idle_time, idle_enter, idle_exit;
unsigned int seq;
do {
- now = get_tod_clock();
seq = read_seqcount_begin(&idle->seqcount);
idle_time = READ_ONCE(idle->idle_time);
idle_enter = READ_ONCE(idle->clock_idle_enter);
idle_exit = READ_ONCE(idle->clock_idle_exit);
} while (read_seqcount_retry(&idle->seqcount, seq));
- idle_time += idle_enter ? ((idle_exit ? : now) - idle_enter) : 0;
+ in_idle = 0;
+ now = get_tod_clock();
+ if (idle_enter) {
+ if (idle_exit) {
+ in_idle = idle_exit - idle_enter;
+ } else if (now > idle_enter) {
+ in_idle = now - idle_enter;
+ }
+ }
+ idle_time += in_idle;
return sprintf(buf, "%llu\n", idle_time >> 12);
}
DEVICE_ATTR(idle_time_us, 0444, show_idle_time, NULL);
@@ -88,17 +96,24 @@ DEVICE_ATTR(idle_time_us, 0444, show_idl
u64 arch_cpu_idle_time(int cpu)
{
struct s390_idle_data *idle = &per_cpu(s390_idle, cpu);
- unsigned long long now, idle_enter, idle_exit;
+ unsigned long long now, idle_enter, idle_exit, in_idle;
unsigned int seq;
do {
- now = get_tod_clock();
seq = read_seqcount_begin(&idle->seqcount);
idle_enter = READ_ONCE(idle->clock_idle_enter);
idle_exit = READ_ONCE(idle->clock_idle_exit);
} while (read_seqcount_retry(&idle->seqcount, seq));
-
- return cputime_to_nsecs(idle_enter ? ((idle_exit ?: now) - idle_enter) : 0);
+ in_idle = 0;
+ now = get_tod_clock();
+ if (idle_enter) {
+ if (idle_exit) {
+ in_idle = idle_exit - idle_enter;
+ } else if (now > idle_enter) {
+ in_idle = now - idle_enter;
+ }
+ }
+ return cputime_to_nsecs(in_idle);
}
void arch_cpu_idle_enter(void)
