Re: [PATCH 3/3] uprobes: make uprobe_register() return struct uprobe *

[Jiri Olsa]

On Wed, Jul 10, 2024 at 11:23:10AM -0700, Andrii Nakryiko wrote:
> On Wed, Jul 10, 2024 at 9:49 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
> >
> > On Wed, Jul 10, 2024 at 06:31:33PM +0200, Oleg Nesterov wrote:
> >
> > SNIP
> >
> > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > > index 467f358c8ce7..7571811127a2 100644
> > > --- a/kernel/trace/bpf_trace.c
> > > +++ b/kernel/trace/bpf_trace.c
> > > @@ -3157,6 +3157,7 @@ struct bpf_uprobe {
> > >       loff_t offset;
> > >       unsigned long ref_ctr_offset;
> > >       u64 cookie;
> > > +     struct uprobe *uprobe;
> > >       struct uprobe_consumer consumer;
> > >  };
> > >
> > > @@ -3180,10 +3181,8 @@ static void bpf_uprobe_unregister(struct path *path, struct bpf_uprobe *uprobes,
> > >  {
> > >       u32 i;
> > >
> > > -     for (i = 0; i < cnt; i++) {
> > > -             uprobe_unregister(d_real_inode(path->dentry), uprobes[i].offset,
> > > -                               &uprobes[i].consumer);
> > > -     }
> >
> > nice, we could also drop path argument now
> 
> see my comments to Oleg, I think we can/should get rid of link->path
> altogether if uprobe itself keeps inode alive.

yea, I was thinking of that, but then it's kind of useful to have it in
bpf_uprobe_multi_link_fill_link_info, otherwise we have to take it from
first uprobe in the link, but ok, still probably worth to remove it ;-)

anyway as you wrote it's ok for follow up cleanup, I'll check on that

> 
> BTW, Jiri, do we have any test for multi-uprobe that simulates partial
> attachment success/failure (whichever way you want to look at it). It
> would be super useful to have to check at least some error handling
> code in the uprobe code base. If we don't, do you mind adding
> something simple to BPF selftests?

there's test_attach_api_fails, but I think all checked fails are before
actually calling uprobe_register function

I think there are few ways to fail the uprobe_register, like install it
on top of int3.. will check add some test for that

jirka

> 
> >
> > jirka
> >
> > > +     for (i = 0; i < cnt; i++)
> > > +             uprobe_unregister(uprobes[i].uprobe, &uprobes[i].consumer);
> > >  }
> > >
> > >  static void bpf_uprobe_multi_link_release(struct bpf_link *link)
> > > @@ -3477,11 +3476,12 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
> > >                     &bpf_uprobe_multi_link_lops, prog);
> > >
> > >       for (i = 0; i < cnt; i++) {
> > > -             err = uprobe_register(d_real_inode(link->path.dentry),
> > > +             uprobes[i].uprobe = uprobe_register(d_real_inode(link->path.dentry),
> > >                                            uprobes[i].offset,
> > >                                            uprobes[i].ref_ctr_offset,
> > >                                            &uprobes[i].consumer);
> > > -             if (err) {
> > > +             if (IS_ERR(uprobes[i].uprobe)) {
> > > +                     err = PTR_ERR(uprobes[i].uprobe);
> > >                       bpf_uprobe_unregister(&path, uprobes, i);
> > >                       goto error_free;
> > >               }