Re: [PATCH perf/core 01/11] uprobes: Add unique flag to uprobe consumer

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Tue,  2 Sep 2025 16:34:54 +0200
Jiri Olsa <jolsa@kernel.org> wrote:

> Adding unique flag to uprobe consumer to ensure it's the only consumer
> attached on the uprobe.
> 
> This is helpful for use cases when consumer wants to change user space
> registers, which might confuse other consumers. With this change we can
> ensure there's only one consumer on specific uprobe.

nit: Does this mean one callback (consumer) is exclusively attached?
If so, "exclusive" will be better wording?

The logic looks good to me.

Thanks,

> 
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>  include/linux/uprobes.h |  1 +
>  kernel/events/uprobes.c | 30 ++++++++++++++++++++++++++++--
>  2 files changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index 08ef78439d0d..0df849dee720 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -60,6 +60,7 @@ struct uprobe_consumer {
>  	struct list_head cons_node;
>  
>  	__u64 id;	/* set when uprobe_consumer is registered */
> +	bool is_unique; /* the only consumer on uprobe */
>  };
>  
>  #ifdef CONFIG_UPROBES
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 996a81080d56..b9b088f7333a 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1024,14 +1024,35 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset,
>  	return uprobe;
>  }
>  
> -static void consumer_add(struct uprobe *uprobe, struct uprobe_consumer *uc)
> +static bool consumer_can_add(struct list_head *head, struct uprobe_consumer *uc)
> +{
> +	/* Uprobe has no consumer, we can add any. */
> +	if (list_empty(head))
> +		return true;
> +	/* Uprobe has consumer/s, we can't add unique one. */
> +	if (uc->is_unique)
> +		return false;
> +	/*
> +	 * Uprobe has consumer/s, we can add nother consumer only if the
> +	 * current consumer is not unique.
> +	 **/
> +	return !list_first_entry(head, struct uprobe_consumer, cons_node)->is_unique;
> +}
> +
> +static int consumer_add(struct uprobe *uprobe, struct uprobe_consumer *uc)
>  {
>  	static atomic64_t id;
> +	int ret = -EBUSY;
>  
>  	down_write(&uprobe->consumer_rwsem);
> +	if (!consumer_can_add(&uprobe->consumers, uc))
> +		goto unlock;
>  	list_add_rcu(&uc->cons_node, &uprobe->consumers);
>  	uc->id = (__u64) atomic64_inc_return(&id);
> +	ret = 0;
> +unlock:
>  	up_write(&uprobe->consumer_rwsem);
> +	return ret;
>  }
>  
>  /*
> @@ -1420,7 +1441,12 @@ struct uprobe *uprobe_register(struct inode *inode,
>  		return uprobe;
>  
>  	down_write(&uprobe->register_rwsem);
> -	consumer_add(uprobe, uc);
> +	ret = consumer_add(uprobe, uc);
> +	if (ret) {
> +		put_uprobe(uprobe);
> +		up_write(&uprobe->register_rwsem);
> +		return ERR_PTR(ret);
> +	}
>  	ret = register_for_each_vma(uprobe, uc);
>  	up_write(&uprobe->register_rwsem);
>  
> -- 
> 2.51.0
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>