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

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, Sep 03, 2025 at 12:11:33AM +0900, Masami Hiramatsu wrote:
> 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?

yes, exclusive is better, will change

thanks,
jirka

> 
> 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>