Re: [PATCH 4/9] rv: Prevent task migration while handling per-CPU events

[Wen Yang <wen.yang@linux.dev>]

The da_implicit_guard() mechanism is a clean way to inject a monitor-
type-specific guard without cluttering the hot-path helpers.


Reviewed-by: Wen Yang <wen.yang@linux.dev>



On 5/12/26 22:02, Gabriele Monaco wrote:
> Tracepoint handlers are now fully preemptible. When a per-CPU monitor
> handles an event, it retrieves the monitor state using a per-CPU
> pointer. If the event itself doesn't disable preemption, the task can
> migrate to a different CPU and we risk updating the wrong monitor.
> 
> Mitigate this by explicitly disabling task migration before acquiring
> the monitor pointer. This cannot guarantee the monitor runs on the
> correct CPU but reduces the race condition window and prevents warnings.
> 
> Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
> ---
>   include/rv/da_monitor.h | 11 +++++++++++
>   1 file changed, 11 insertions(+)
> 
> diff --git a/include/rv/da_monitor.h b/include/rv/da_monitor.h
> index 0b7028df08fb..a9fd284195ee 100644
> --- a/include/rv/da_monitor.h
> +++ b/include/rv/da_monitor.h
> @@ -181,6 +181,10 @@ static inline void da_monitor_destroy(void)
>   	da_monitor_reset_all();
>   }
>   
> +#ifndef da_implicit_guard
> +#define da_implicit_guard()
> +#endif
> +
>   #elif RV_MON_TYPE == RV_MON_PER_CPU
>   /*
>    * Functions to define, init and get a per-cpu monitor.
> @@ -230,6 +234,10 @@ static inline void da_monitor_destroy(void)
>   	da_monitor_reset_all();
>   }
>   
> +#ifndef da_implicit_guard
> +#define da_implicit_guard() guard(migrate)()
> +#endif
> +
>   #elif RV_MON_TYPE == RV_MON_PER_TASK
>   /*
>    * Functions to define, init and get a per-task monitor.
> @@ -677,6 +685,7 @@ static inline bool __da_handle_start_run_event(struct da_monitor *da_mon,
>    */
>   static inline void da_handle_event(enum events event)
>   {
> +	da_implicit_guard();
>   	__da_handle_event(da_get_monitor(), event, 0);
>   }
>   
> @@ -692,6 +701,7 @@ static inline void da_handle_event(enum events event)
>    */
>   static inline bool da_handle_start_event(enum events event)
>   {
> +	da_implicit_guard();
>   	return __da_handle_start_event(da_get_monitor(), event, 0);
>   }
>   
> @@ -703,6 +713,7 @@ static inline bool da_handle_start_event(enum events event)
>    */
>   static inline bool da_handle_start_run_event(enum events event)
>   {
> +	da_implicit_guard();
>   	return __da_handle_start_run_event(da_get_monitor(), event, 0);
>   }
>