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

On Tue, Aug 27, 2024 at 06:45:45PM +0200, Oleg Nesterov wrote:

On 08/27, Jiri Olsa wrote:

quoted

On Tue, Aug 27, 2024 at 12:29:38AM +0200, Oleg Nesterov wrote:

quoted

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

...

quoted

   ->     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
	}

quoted

I think the uretprobe_dispatcher could call filter as suggested in the original
patch..

OK, agreed.

quoted

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.