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

    * 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


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