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| author | Heiko Carstens <heiko.carstens@de.ibm.com> | 2019-10-28 13:03:27 +0300 |
|---|---|---|
| committer | Vasily Gorbik <gor@linux.ibm.com> | 2019-10-31 19:26:48 +0300 |
| commit | 3d7efa4edd07be5c5c3ffa95ba63e97e070e1f3f (patch) | |
| tree | 7b086d413d56374438633850d74f14bf82846581 /arch | |
| parent | a1d863ac3e1085e1fea9caafd87252d08731de2e (diff) | |
| download | linux-3d7efa4edd07be5c5c3ffa95ba63e97e070e1f3f.tar.xz | |
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.c | 29 |
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) |