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authorHeiko Carstens <heiko.carstens@de.ibm.com>2019-10-28 11:03:27 +0100
committerVasily Gorbik <gor@linux.ibm.com>2019-10-31 17:26:48 +0100
commit3d7efa4edd07be5c5c3ffa95ba63e97e070e1f3f (patch)
tree7b086d413d56374438633850d74f14bf82846581 /arch
parents390/unwind: fix mixing regs and sp (diff)
downloadlinux-3d7efa4edd07be5c5c3ffa95ba63e97e070e1f3f.tar.xz
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s390/idle: fix cpu idle time calculation
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@vger.kernel.org> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/s390/kernel/idle.c29
1 files changed, 22 insertions, 7 deletions
diff --git a/arch/s390/kernel/idle.c b/arch/s390/kernel/idle.c
index b9d8fe45737a..8f8456816d83 100644
--- a/arch/s390/kernel/idle.c
+++ b/arch/s390/kernel/idle.c
@@ -69,18 +69,26 @@ DEVICE_ATTR(idle_count, 0444, show_idle_count, NULL);
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_idle_time, NULL);
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)