Re: [bpf?] [net-next ?] [RESEND] possible bpf overflow/output bug introduced in 6.10rc1 ?

[Kyle Huey]

On Fri, Jul 12, 2024 at 5:45 PM Joe Damato <jdamato@xxxxxxxxxx> wrote:
>
> On Fri, Jul 12, 2024 at 04:30:31PM -0700, Kyle Huey wrote:
> > Joe, can you test this?
> >
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 8f908f077935..f0d7119585dc 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -9666,6 +9666,8 @@ static inline void
> > perf_event_free_bpf_handler(struct perf_event *event)
> >   * Generic event overflow handling, sampling.
> >   */
> >
> > +static bool perf_event_is_tracing(struct perf_event *event);
> > +
> >  static int __perf_event_overflow(struct perf_event *event,
> >                   int throttle, struct perf_sample_data *data,
> >                   struct pt_regs *regs)
> > @@ -9682,7 +9684,9 @@ static int __perf_event_overflow(struct perf_event *event,
> >
> >      ret = __perf_event_account_interrupt(event, throttle);
> >
> > -    if (event->prog && !bpf_overflow_handler(event, data, regs))
> > +    if (event->prog &&
> > +        !perf_event_is_tracing(event) &&
> > +        !bpf_overflow_handler(event, data, regs))
> >          return ret;
> >
> >      /*
> > @@ -10612,6 +10616,11 @@ void perf_event_free_bpf_prog(struct perf_event *event)
> >
> >  #else
> >
> > +static inline bool perf_event_is_tracing(struct perf_event *event)
> > +{
> > +    return false;
> > +}
> > +
> >  static inline void perf_tp_register(void)
> >  {
> >  }
> >
>
> Thank you!
>
> I've applied the above patch on top of commit 338a93cf4a18 ("net:
> mctp-i2c: invalidate flows immediately on TX errors"), which seems
> to be latest on net-next/main.
>
> I built and booted that kernel on my mlx5 test machine and re-ran
> the same bpftrace invocation:
>
>   bpftrace -e 'tracepoint:napi:napi_poll { @[args->work] = count(); }'
>
> I then scp-ed a 100MiB zero filled file to the target 48 times back
> to back (e.g. scp zeroes target:~/ && scp zeroes target:~/ && ... )
> and the bpftrace output seems reasonable; there are no negative
> numbers and the values output *look* reasonable to me.
>
> The patch seems reasonable, as well, with the major caveat that I've
> only hacked on drivers and networking stuff and know absolutely
> nothing about bpf internals.
>
> All that said:
>
> Tested-by: Joe Damato <jdamato@xxxxxxxxxx>

Thanks, I've sent a patch formally.

Hopefully this can slip into 6.10 before it ships.

- Kyle