On Thu, Jan 10, 2019 at 05:17:16PM -0800, Stephane Eranian wrote:
> The perf_proc_update_handler() handles
> /proc/sys/kernel/perf_event_max_sample_rate
> syctl variable. When the PMU IRQ handler timing monitoring is disabled, i.e,
> when /proc/sys/kernel/perf_cpu_time_max_percent is equal to 0 or 100,
> then no modification to sysctl_perf_event_sample_rate is allowed to prevent
> possible hang from wrong values.
>
> The problem is that the test to prevent modification is made after the
> sysctl variable is modified in perf_proc_update_handler().
>
> You get an error:
>
> $ echo 10001 >/proc/sys/kernel/perf_event_max_sample_rate
> echo: write error: invalid argument
>
> But the value is still modified causing all sorts of inconsistencies:
>
> $ cat /proc/sys/kernel/perf_event_max_sample_rate
> 10001
>
> This patch fixes the problem by moving the parsing of the value after
> the test.
>
> Signed-off-by: Stephane Eranian <eran...@google.com>
Reviewed-by: Jiri Olsa <jo...@kernel.org>
jirka
> ---
> kernel/events/core.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 3cd13a30f732..e5ede6918050 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -436,18 +436,18 @@ int perf_proc_update_handler(struct ctl_table *table,
> int write,
> void __user *buffer, size_t *lenp,
> loff_t *ppos)
> {
> - int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
> -
> - if (ret || !write)
> - return ret;
> -
> + int ret;
> + int perf_cpu = sysctl_perf_cpu_time_max_percent;
> /*
> * If throttling is disabled don't allow the write:
> */
> - if (sysctl_perf_cpu_time_max_percent == 100 ||
> - sysctl_perf_cpu_time_max_percent == 0)
> + if (write && (perf_cpu == 100 || perf_cpu == 0))
> return -EINVAL;
>
> + ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
> + if (ret || !write)
> + return ret;
> +
> max_samples_per_tick = DIV_ROUND_UP(sysctl_perf_event_sample_rate, HZ);
> perf_sample_period_ns = NSEC_PER_SEC / sysctl_perf_event_sample_rate;
> update_perf_cpu_limits();
> --
> 2.7.4
>
