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

[Andrii Nakryiko]

On Wed, Jul 10, 2024 at 12:38 PM Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
>
> 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 ;-)

if we need it for link_info, probably cleaner to just keep it, no big deal then

>
> 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
>

great, thank you!

> 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;
> > > >               }