Re: [PATCH RESEND v4] perf/core: Fix reentry problem in perf_output_read_group

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Sep 02, 2022 at 04:29:18PM +0800, Yang Jihong wrote:
> perf_output_read_group may respond to IPI request of other cores and invoke
> __perf_install_in_context function. As a result, hwc configuration is modified.
> causing inconsistency and unexpected consequences.
> 
> Interrupts are not disabled when perf_output_read_group reads PMU counter.
> In this case, IPI request may be received from other cores.
> As a result, PMU configuration is modified and an error occurs when
> reading PMU counter:
> 
>                    CPU0                                         CPU1
>                                                     __se_sys_perf_event_open
>                                                       perf_install_in_context
> perf_output_read_group                                  smp_call_function_single
>   for_each_sibling_event(sub, leader) {                   generic_exec_single
>     if ((sub != event) &&                                   remote_function
>         (sub->state == PERF_EVENT_STATE_ACTIVE))                    |
> <enter IPI handler: __perf_install_in_context>   <----RAISE IPI-----+
> __perf_install_in_context
>   ctx_resched
>     event_sched_out
>       armpmu_del
>         ...
>         hwc->idx = -1; // event->hwc.idx is set to -1
> ...
> <exit IPI>
>             sub->pmu->read(sub);
>               armpmu_read
>                 armv8pmu_read_counter
>                   armv8pmu_read_hw_counter
>                     int idx = event->hw.idx; // idx = -1
>                     u64 val = armv8pmu_read_evcntr(idx);
>                       u32 counter = ARMV8_IDX_TO_COUNTER(idx); // invalid counter = 30
>                       read_pmevcntrn(counter) // undefined instruction
> 
> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
> ---

Right; thanks for reminding me. I had hoped you'd pick up and test the
extra assertion some, but I'll just do that on top.