Re: [PATCH v4 4/8] uprobes: travers uprobe's consumer list locklessly under SRCU protection

[Oleg Nesterov <oleg@redhat.com>]

On 09/03, Andrii Nakryiko wrote:
>
> On Sat, Aug 31, 2024 at 9:19 AM Oleg Nesterov <oleg@redhat.com> wrote:
> >
> > I was thinking about another seq counter incremented in register(), so
> > that handler_chain() can detect the race with uprobe_register() and skip
> > unapply_uprobe() in this case. This is what Peter did in one of his series.
> > Still changes the current behaviour, but not too much.
>
> We could do that, but then worst case, when we do detect registration
> race, what do we do?

Do nothing and skip unapply_uprobe().

> But as you said, this all can/should be addressed as a follow up
> discussion.

Yes, yes,

> You mentioned some clean ups you wanted to do, let's
> discuss all that as part of that?

Yes, sure.

And please note that in reply to myself I also mentioned that I am stupid
and these cleanups can't help to change/improve this behaviour ;)

> > The only in-kernel user of UPROBE_HANDLER_REMOVE is perf, and it is fine.
> >
>
> Well, BPF program can accidentally trigger this as well, but that's a
> bug, we should fix it ASAP in the bpf tree.

not sure, but...

> > And in general, this change makes the API less "flexible".
>
> it maybe makes a weird and too-flexible case a bit more work to
> implement. Because if consumer want to be that flexible, they can
> still define filter that will be coordinated between filter() and
> handler() implementation.

perhaps, but lets discuss this later, on top of your series.

> > But once again, I agree that it would be better to apply your series first,
> > then add the fixes in (unlikely) case it breaks something.
>
> Yep, agreed, thanks! Will send a new version ASAP, so we have a common
> base to work on top of.

Thanks. Hopefully Peter will queue your V5 soon.

Oleg.