Re: [PATCH v2] tracing/uprobe: Add missing PID filter for uretprobe

[Jiri Olsa <olsajiri@gmail.com>]

On Tue, Aug 27, 2024 at 04:26:08PM +0200, Oleg Nesterov wrote:
> On 08/27, Jiri Olsa wrote:
> >
> > On Tue, Aug 27, 2024 at 12:40:52PM +0200, Oleg Nesterov wrote:
> > >  static bool
> > >  uprobe_multi_link_filter(struct uprobe_consumer *con, struct mm_struct *mm)
> > >  {
> > >  	struct bpf_uprobe *uprobe;
> > > +	struct task_struct *task, *t;
> > > +	bool ret = false;
> > >
> > >  	uprobe = container_of(con, struct bpf_uprobe, consumer);
> > > -	return uprobe->link->task->mm == mm;
> > > +	task = uprobe->link->task;
> > > +
> > > +	rcu_read_lock();
> > > +	for_each_thread(task, t) {
> > > +		struct mm_struct *mm = READ_ONCE(t->mm);
> > > +		if (mm) {
> > > +			ret = t->mm == mm;
> > > +			break;
> > > +		}
> > > +	}
> > > +	rcu_read_unlock();
> >
> > that seems expensive if there's many threads
> 
> many threads with ->mm == NULL? In the likely case for_each_thread()
> stops after the first t->mm check.

aah the mm will be the same.. right, nice

thanks,
jirka