[v1] trace/osnoise: prevent osnoise hotplog worker running in UNBOUND workqueue

[v1] trace/osnoise: prevent osnoise hotplog worker running in UNBOUND workqueue

[Andy Chiu]

smp_processor_id() should be called with migration disabled. This mean
we may safely call smp_processor_id() in percpu thread. However, this is
not the case if the work is (re-)queued into unbound workqueue, during
cpu-hotplog. So, detect and return early if this work happens to run on
an unbound wq.

Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
---
 kernel/trace/trace_osnoise.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index bd0d01d00fb9..cf7f716d3f35 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -2068,7 +2068,12 @@ static int start_per_cpu_kthreads(void)
 #ifdef CONFIG_HOTPLUG_CPU
 static void osnoise_hotplug_workfn(struct work_struct *dummy)
 {
-	unsigned int cpu = smp_processor_id();
+	unsigned int cpu;
+
+	if (!is_percpu_thread())
+		return;
+
+	cpu = smp_processor_id();
 
 	mutex_lock(&trace_types_lock);
 
-- 
2.43.0

Re: [v1] trace/osnoise: prevent osnoise hotplog worker running in UNBOUND workqueue

[Steven Rostedt]

On Thu,  1 Feb 2024 14:18:45 +0800
Andy Chiu <andy.chiu@sifive.com> wrote:

> smp_processor_id() should be called with migration disabled. This mean
> we may safely call smp_processor_id() in percpu thread. However, this is
> not the case if the work is (re-)queued into unbound workqueue, during
> cpu-hotplog. So, detect and return early if this work happens to run on
> an unbound wq.
> 

Yeah I triggered this too, but never made it a priority to fix.


> Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
> ---
>  kernel/trace/trace_osnoise.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
> index bd0d01d00fb9..cf7f716d3f35 100644
> --- a/kernel/trace/trace_osnoise.c
> +++ b/kernel/trace/trace_osnoise.c
> @@ -2068,7 +2068,12 @@ static int start_per_cpu_kthreads(void)
>  #ifdef CONFIG_HOTPLUG_CPU
>  static void osnoise_hotplug_workfn(struct work_struct *dummy)
>  {
> -	unsigned int cpu = smp_processor_id();
> +	unsigned int cpu;
> +
> +	if (!is_percpu_thread())
> +		return;

But doesn't this then fail to register the CPU thread?

I wonder if this has some race with schedule_work_on() and hotplug?

-- Steve



> +
> +	cpu = smp_processor_id();
>  
>  	mutex_lock(&trace_types_lock);
>