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

On 08/26, Jiri Olsa wrote:

On Mon, Aug 26, 2024 at 01:57:52PM +0200, Oleg Nesterov wrote:

quoted

On 08/26, Jiri Olsa wrote:

quoted

quoted

But "perf-record -p" works as expected.

I wonder it's because there's the perf layer that schedules each
uprobe event only when its process (PID1/2) is scheduled in and will
receive events only from that cpu while the process is running on it

Not sure I understand... The task which hits the breakpoint is always
current, it is always scheduled in.

hum, I might be missing something, but ;-)

No it is me ;) at least I certainly misunderstood your "scheduled in".

assuming we have 2 tasks, each with perf uprobe event assigned

in perf path there's uprobe_perf_func which calls the uprobe_perf_filter
and if it returns true it then goes:

  uprobe_perf_func
    __uprobe_perf_func
      perf_trace_buf_submit
        perf_tp_event
        {

           hlist_for_each_entry_rcu(event, head, hlist_entry) {
             if (perf_tp_event_match(event, &data, regs)) {
                perf_swevent_event(event, count, &data, regs);

Aha. So, in this particular case, when the CLONE_VM child hits the bp
and calls uprobe_perf_func(), even perf_tp_event_match() won't be called,
head is hlist_empty(), right?

Thanks!

in comparison with uprobe_multi path, where uprobe_multi_link_filter

Yeah, this is clear.

quoted

IIUC (but I am not sure), perf-record -p will work "correctly" even if we
remove uprobe_perf_filter() altogether. IIRC the perf layer does its own
filtering but I forgot everything.

I think that's what I tried to describe above

Yes, thanks.

Oleg.