On Tue, 15 Jun 2021 11:28:44 +0200
Daniel Bristot de Oliveira <bristot@xxxxxxxxxx> wrote:
> Enable and disable hwlat thread during cpu hotplug online
> and offline operations, respectivelly.
>
> Cc: Jonathan Corbet <corbet@xxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
> Cc: Clark Willaims <williams@xxxxxxxxxx>
> Cc: John Kacur <jkacur@xxxxxxxxxx>
> Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Cc: linux-doc@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
> ---
> kernel/trace/trace.c | 6 ++++++
> kernel/trace/trace_hwlat.c | 34 ++++++++++++++++++++++++++++++++++
> 2 files changed, 40 insertions(+)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 9299057feb56..c094865e2f71 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -5064,7 +5064,13 @@ int tracing_set_cpumask(struct trace_array *tr,
> arch_spin_unlock(&tr->max_lock);
> local_irq_enable();
>
> + /*
> + * tracing_cpumask is read by tracers that support CPU
> + * hotplug.
> + */
> + get_online_cpus();
> cpumask_copy(tr->tracing_cpumask, tracing_cpumask_new);
> + put_online_cpus();
>
> return 0;
> }
> diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
> index 6c6918e86087..9fcfd588c4f6 100644
> --- a/kernel/trace/trace_hwlat.c
> +++ b/kernel/trace/trace_hwlat.c
> @@ -490,6 +490,35 @@ static int start_cpu_kthread(unsigned int cpu)
> return 0;
> }
>
> +/*
> + * hwlat_cpu_init - CPU hotplug online callback function
> + */
> +static int hwlat_cpu_init(unsigned int cpu)
> +{
> + struct trace_array *tr = hwlat_trace;
> +
You need to take the trace_types_lock here, between testing the
hwlat_busy and starting the threads. Otherwise, between the two, the
hwlat tracer could be turned off while a CPU is coming on line, and
then you just started a per cpu thread, while the hwlat tracer is not
enabled.
> + if (!hwlat_busy)
> + return 0;
> +
> + if (!cpumask_test_cpu(cpu, tr->tracing_cpumask))
> + return 0;
> +
> + return start_cpu_kthread(cpu);
> +}
> +
> +/*
> + * hwlat_cpu_die - CPU hotplug offline callback function
> + */
> +static int hwlat_cpu_die(unsigned int cpu)
> +{
Same here.
-- Steve
> + if (!hwlat_busy)
> + return 0;
> +
> + stop_cpu_kthread(cpu);
> +
> + return 0;
> +}
> +
> /*
> * start_per_cpu_kthreads - Kick off the hardware latency sampling/detector kthreads
> *
> @@ -903,6 +932,11 @@ __init static int init_hwlat_tracer(void)
> if (ret)
> return ret;
>
> + ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "trace/hwlat:online",
> + hwlat_cpu_init, hwlat_cpu_die);
> + if (ret < 0)
> + pr_warn(BANNER "Error to init cpu hotplug support\n");
> +
> init_tracefs();
>
> return 0;
