Re: [RFC/PATCH bpf-next] bpf: Fix d_path test after last fs update

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On Wed, Aug 30, 2023 at 9:27 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
>
> On Wed, Aug 30, 2023 at 11:35:02AM +0200, Jiri Olsa wrote:
> > Recent commit [1] broken d_path test, because now filp_close is not
> > called directly from sys_close, but eventually later when the file
> > is finally released.
> >
> > I can't see any other solution than to hook filp_flush function and
> > that also means we need to add it to btf_allowlist_d_path list, so
> > it can use the d_path helper.
> >
> > But it's probably not very stable because filp_flush is static so it
> > could be potentially inlined.
>
> looks like llvm makes it inlined (from CI)
>
>   Error: #68/1 d_path/basic
>   libbpf: prog 'prog_close': failed to find kernel BTF type ID of 'filp_flush': -3
>
> jirka

I played with it for a bit, but haven't got a good solution. Maybe we should
just remove the test for close()?

Thanks,
Song
>
> >
> > Also if we'd keep the current filp_close hook and find a way how to 'wait'
> > for it to be called so user space can go with checks, then it looks
> > like d_path might not work properly when the task is no longer around.

[...]





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