Re: [PATCH 1/4] tracing: Use the perf recursion protection from trace event

Ingo Molnar
2009-11-22T11:23:10Z

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Sun, 2009-11-22 at 05:21 +0100, Frederic Weisbecker wrote:
> > diff --git a/kernel/perf_event.c b/kernel/perf_event.c
> > index 718fa93..aba8227 100644
> > --- a/kernel/perf_event.c
> > +++ b/kernel/perf_event.c
> > @@ -3880,34 +3880,42 @@ static void perf_swevent_ctx_event(struct perf_event_context *ctx,
> > }
> > }
> >
> > -static int *perf_swevent_recursion_context(struct perf_cpu_context *cpuctx)
> > +/*
> > + * Must be called with preemption disabled
> > + */
> > +int perf_swevent_get_recursion_context(int **recursion)
> > {
> > + struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
> > +
> > if (in_nmi())
> > - return &cpuctx->recursion[3];
> > + *recursion = &cpuctx->recursion[3];
> > + else if (in_irq())
> > + *recursion = &cpuctx->recursion[2];
> > + else if (in_softirq())
> > + *recursion = &cpuctx->recursion[1];
> > + else
> > + *recursion = &cpuctx->recursion[0];
> >
> > - if (in_irq())
> > - return &cpuctx->recursion[2];
> > + if (**recursion)
> > + return -1;
> >
> > - if (in_softirq())
> > - return &cpuctx->recursion[1];
> > + (**recursion)++;
> >
> > - return &cpuctx->recursion[0];
> > + return 0;
> > }
>
> You lost the barrier();
>
> > -static void do_perf_sw_event(enum perf_type_id type, u32 event_id,
> > - u64 nr, int nmi,
> > - struct perf_sample_data *data,
> > - struct pt_regs *regs)
> > +void perf_swevent_put_recursion_context(int *recursion)
> > {
> > - struct perf_cpu_context *cpuctx = &get_cpu_var(perf_cpu_context);
> > - int *recursion = perf_swevent_recursion_context(cpuctx);
> > - struct perf_event_context *ctx;
> > -
> > - if (*recursion)
> > - goto out;
> > + (*recursion)--;
> > +}
>
> And here as well.

Global functions are in essence a barrier() to GCC but yeah.

Ingo