Re: [PATCH 05/10] perf/uprobe: SRCU-ify uprobe->consumer list

[Peter Zijlstra]

On Mon, Jul 08, 2024 at 11:12:46AM +0200, Peter Zijlstra wrote:
> @@ -2087,14 +2092,19 @@ static struct uprobe *find_active_uprobe
>  	return uprobe;
>  }
>  
> +#define for_each_consumer_rcu(pos, head) \
> +	for (pos = rcu_dereference_raw(head); pos; \
> +	     pos = rcu_dereference_raw(pos->next))
> +
>  static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
>  {
>  	struct uprobe_consumer *uc;
>  	int remove = UPROBE_HANDLER_REMOVE;
>  	bool need_prep = false; /* prepare return uprobe, when needed */
>  
> -	down_read(&uprobe->register_rwsem);
> -	for (uc = uprobe->consumers; uc; uc = uc->next) {
> +	guard(srcu)(&uprobes_srcu);
> +
> +	for_each_consumer_rcu(uc, uprobe->consumers) {
>  		int rc = 0;
>  
>  		if (uc->handler) {
> @@ -2116,7 +2126,6 @@ static void handler_chain(struct uprobe
>  		WARN_ON(!uprobe_is_active(uprobe));
>  		unapply_uprobe(uprobe, current->mm);

   ^^^ this remove case needs more thought.

>  	}
> -	up_read(&uprobe->register_rwsem);
>  }