Messages in this thread | | | Date | Fri, 18 Jun 2021 12:45:03 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH V4 05/12] trace/hwlat: Support hotplug operations |
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On Tue, 15 Jun 2021 11:28:44 +0200 Daniel Bristot de Oliveira <bristot@redhat.com> wrote:
> Enable and disable hwlat thread during cpu hotplug online > and offline operations, respectivelly. > > Cc: Jonathan Corbet <corbet@lwn.net> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Alexandre Chartre <alexandre.chartre@oracle.com> > Cc: Clark Willaims <williams@redhat.com> > Cc: John Kacur <jkacur@redhat.com> > Cc: Juri Lelli <juri.lelli@redhat.com> > Cc: Borislav Petkov <bp@alien8.de> > Cc: "H. Peter Anvin" <hpa@zytor.com> > Cc: x86@kernel.org > Cc: linux-doc@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com> > --- > 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;
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