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

[Oleg Nesterov <oleg@redhat.com>]

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

	// 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.