On Sat, Apr 30, 2022 at 5:30 AM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
>
> On Tue, Apr 26, 2022 at 12:52 AM Benjamin Tissoires
> <benjamin.tissoires@xxxxxxxxxx> wrote:
> >
> > On Tue, Apr 26, 2022 at 6:11 AM Alexei Starovoitov
> > <alexei.starovoitov@xxxxxxxxx> wrote:
> > >
> > > On Thu, Apr 21, 2022 at 04:07:36PM +0200, Benjamin Tissoires wrote:
> > > > When using error-injection function through bpf to change the return
> > > > code, we need to know if the function is sleepable or not.
> > > >
> > > > Currently the code assumes that all error-inject functions are sleepable,
> > > > except for a few selected of them, hardcoded in kernel/bpf/verifier.c
> > > >
> > > > Add a new flag to error-inject so we can code that information where the
> > > > function is declared.
> > > >
> > > > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx>
> > > >
> > > > ---
> > > >
> > > > new in v4:
> > > > - another approach would be to define a new kfunc_set, and register
> > > > it with btf. But in that case, what program type would we use?
> > > > BPF_PROG_TYPE_UNSPEC?
> > > > - also note that maybe we should consider all of the functions
> > > > non-sleepable and only mark some as sleepable. IMO it makes more
> > > > sense to be more restrictive by default.
> > >
> > > I think the approach in this patch is fine.
> > > We didn't have issues with check_non_sleepable_error_inject() so far,
> > > so I wouldn't start refactoring it.
> >
> > OK... though I can't help but thinking that adding a new
> > error-inject.h enum value is going to be bad, because it's an API
> > change, and users might not expect NS_ERRNO.
>
> Not sure about api concern. This is the kernel internal tag.
> bpf progs are not aware of them. The functions can change
> from sleepable to non-sleepable too.
> allow_error_inject can be removed. And so on.
>
> > OTOH, if we had a new kfunc_set, we keep the existing error-inject API
> > in place with all the variants and we just teach the verifier that the
> > function is non sleepable.
> ...
> > IIUC, the kfunc_set approach would solve that, no?
>
> Makes sense. Let's figure out an extensible kfunc_set approach
> that is not centralized in verifier.c
>
OK, I'll work on this in v5.
But I need to rethink the whole sleepable/non-sleepable definitions
for my use case, because I have now a clear separation between not
sleepable context (in fentry/fexit/fmod_ret) and sleepable context (in
SEC("syscall")), so maybe the whole thing is not really required.
Cheers,
Benjamin
