Re: [PATCH 5/9] rv: Ensure all pending probes terminate on per-obj monitor destroy

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

Correct for PER_OBJ: kfree() is called directly (not kfree_rcu()) after
hash_del_rcu(), so we must guarantee no concurrent reader holds a 
pointer to mon_storage.  tracepoint_synchronize_unregister() — which 
calls synchronize_rcu_tasks_trace() then synchronize_srcu  —
drains all in-flight probe handlers before the hash walk, making the
subsequent kfree() safe.


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



On 5/12/26 22:02, Gabriele Monaco wrote:
> The monitor disable/destroy sequence detaches all probes and resets the
> monitor's data, however it doesn't wait for pending probes. This is an
> issue with per-object monitors, which free the monitor storage.
> 
> Call tracepoint_synchronize_unregister() to make sure to wait for all
> pending probes before destroying the monitor storage.
> 
> Fixes: 4a24127bd6cb ("rv: Add support for per-object monitors in DA/HA")
> Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
> ---
>   include/rv/da_monitor.h | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/include/rv/da_monitor.h b/include/rv/da_monitor.h
> index a9fd284195ee..a4a13b62d1a4 100644
> --- a/include/rv/da_monitor.h
> +++ b/include/rv/da_monitor.h
> @@ -515,9 +515,10 @@ static inline void da_monitor_destroy(void)
>   	struct hlist_node *tmp;
>   	int bkt;
>   
> +	tracepoint_synchronize_unregister();
>   	/*
> -	 * This function is called after all probes are disabled, we need only
> -	 * worry about concurrency against old events.
> +	 * This function is called after all probes are disabled and no longer
> +	 * pending, we can safely assume no concurrent user.
>   	 */
>   	synchronize_rcu();
>   	hash_for_each_safe(da_monitor_ht, bkt, tmp, mon_storage, node) {