linux-kernel - Re: [PATCH v2 net-next 4/6] perf, bpf: add perf events core support for BPF_PROG_TYPE_PERF

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Date:   Thu, 1 Sep 2016 08:53:51 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Alexei Starovoitov <ast@...com>,
        "David S . Miller" <davem@...emloft.net>,
        Brendan Gregg <bgregg@...flix.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Arnaldo Carvalho de Melo <acme@...radead.org>,
        Wang Nan <wangnan0@...wei.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH v2 net-next 4/6] perf, bpf: add perf events core support
 for BPF_PROG_TYPE_PERF_EVENT programs

On Thu, Sep 01, 2016 at 10:12:51AM +0200, Peter Zijlstra wrote:
> On Wed, Aug 31, 2016 at 02:50:41PM -0700, Alexei Starovoitov wrote:
> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> > index 97bfe62f30d7..dcaaaf3ec8e6 100644
> > --- a/include/linux/perf_event.h
> > +++ b/include/linux/perf_event.h
> > @@ -679,6 +679,8 @@ struct perf_event {
> >  	u64				(*clock)(void);
> >  	perf_overflow_handler_t		overflow_handler;
> >  	void				*overflow_handler_context;
> 
> > +	perf_overflow_handler_t		orig_overflow_handler;
> > +	struct bpf_prog			*prog;
> 
> Should we put that under CONFIG_BPF_SYSCALL too?

sure. will do.

> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 3cfabdf7b942..305433ab2447 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> 
> > @@ -7637,11 +7637,75 @@ static void perf_event_free_filter(struct perf_event *event)
> >  	ftrace_profile_free_filter(event);
> >  }
> >  
> > +static void bpf_overflow_handler(struct perf_event *event,
> > +				 struct perf_sample_data *data,
> > +				 struct pt_regs *regs)
> > +{
> > +	struct bpf_perf_event_data_kern ctx = {
> > +		.data = data,
> > +		.regs = regs,
> > +	};
> > +	int ret = 0;
> > +
> > +#ifdef CONFIG_BPF_SYSCALL
> > +	preempt_disable();
> > +	if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1))
> > +		goto out;
> > +	rcu_read_lock();
> > +	ret = BPF_PROG_RUN(event->prog, (void *)&ctx);
> > +	rcu_read_unlock();
> > + out:
> 
> Please, no leading space before labels. Use something like:

good catch.
sadly checkpatch didn't complain.
 
> [diff "default"]
>         xfuncname = "^[[:alpha:]$_].*[^:]$"
> 
> In your .gitconfig if you want to keep diff output 'sane'.

interesting trick. don't remember being bitten by it.
This extra space was a typo.

> > +	__this_cpu_dec(bpf_prog_active);
> > +	preempt_enable();
> > +#endif
> > +	if (!ret)
> > +		return;
> > +
> > +	event->orig_overflow_handler(event, data, regs);
> > +}
> 
> Other than that, ACK.

Thanks!