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

[Jiri Olsa <olsajiri@gmail.com>]

On Tue, Aug 27, 2024 at 06:45:45PM +0200, Oleg Nesterov wrote:
> On 08/27, Jiri Olsa wrote:
> >
> > On Tue, Aug 27, 2024 at 12:29:38AM +0200, Oleg Nesterov wrote:
> > >
> > > So, can you reproduce the problem reported by Tianyi on your setup?
> >
> > yes, I can repduce the issue with uretprobe on top of perf event uprobe
> 
> ...
> 
> >    ->     uretprobe-hit
> >             handle_swbp
> >               uprobe_handle_trampoline
> >                 handle_uretprobe_chain
> >                 {
> >
> >                   for_each_uprobe_consumer {
> >
> >                     // consumer for task 1019
> >                     uretprobe_dispatcher
> >                       uretprobe_perf_func
> >                         -> runs bpf program
> >
> >                     // consumer for task 1018
> >                     uretprobe_dispatcher
> >                       uretprobe_perf_func
> >                         -> runs bpf program
> 
> Confused...
> 
> I naively thought that if bpftrace uses bpf_uprobe_multi_link_attach() then
> it won't use perf/trace_uprobe, and uretprobe-hit will result in

right, this path is for the case when bpftrace attach to single uprobe,
but there are 2 instances of bpftrace 

jirka

> 
> 	// current->pid == 1018
> 
> 	for_each_uprobe_consumer {
> 		// consumer for task 1019
> 		uprobe_multi_link_ret_handler
> 		    uprobe_prog_run
> 		       -> current->mm != link->task->mm, return
> 
> 		// consumer for task 1018
> 		uprobe_multi_link_ret_handler
> 		    uprobe_prog_run
> 		       -> current->mm == link->task->mm, run bpf
> 	}
> 
> > I think the uretprobe_dispatcher could call filter as suggested in the original
> > patch..
> 
> OK, agreed.
> 
> > but I'm not sure we need to remove the uprobe from handle_uretprobe_chain
> > like we do in handler_chain..
> 
> Me too. In any case this is another issue.
> 
> Oleg.
>