Re: [PATCH V3 4/7] driver/perf/arm_pmu_platform: Add support for BRBE attributes detection

[James Clark <james.clark@arm.com>]

On 29/09/2022 08:58, Anshuman Khandual wrote:
> This adds arm pmu infrastrure to probe BRBE implementation's attributes via
> driver exported callbacks later. The actual BRBE feature detection will be
> added by the driver itself.
> 
> CPU specific BRBE entries, cycle count, format support gets detected during
> PMU init. This information gets saved in per-cpu struct pmu_hw_events which
> later helps in operating BRBE during a perf event context.
> 
> Cc: Will Deacon <will@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
>  drivers/perf/arm_pmu_platform.c | 34 +++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
> 
> diff --git a/drivers/perf/arm_pmu_platform.c b/drivers/perf/arm_pmu_platform.c
> index 933b96e243b8..acdc445081aa 100644
> --- a/drivers/perf/arm_pmu_platform.c
> +++ b/drivers/perf/arm_pmu_platform.c
> @@ -172,6 +172,36 @@ static int armpmu_request_irqs(struct arm_pmu *armpmu)
>  	return err;
>  }
>  
> +static void arm_brbe_probe_cpu(void *info)
> +{
> +	struct pmu_hw_events *hw_events;
> +	struct arm_pmu *armpmu = info;
> +
> +	/*
> +	 * Return from here, if BRBE driver has not been
> +	 * implemented for this PMU. This helps prevent
> +	 * kernel crash later when brbe_probe() will be
> +	 * called on the PMU.
> +	 */
> +	if (!armpmu->brbe_probe)
> +		return;
> +
> +	hw_events = per_cpu_ptr(armpmu->hw_events, smp_processor_id());
> +	armpmu->brbe_probe(hw_events);
> +}
> +
> +static int armpmu_request_brbe(struct arm_pmu *armpmu)
> +{
> +	int cpu, err = 0;
> +
> +	for_each_cpu(cpu, &armpmu->supported_cpus) {
> +		err = smp_call_function_single(cpu, arm_brbe_probe_cpu, armpmu, 1);

Hi Anshuman,

I have LOCKDEP on and the patchset applied to perf/core (82aad7ff7) on
git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git and I get
this:

   armv8-pmu pmu: hw perfevents: no interrupt-affinity property, guessing.
   brbe: implementation found on cpu 0

   =============================
   [ BUG: Invalid wait context ]
   6.0.0-rc7 #38 Not tainted
   -----------------------------
   kworker/u8:0/9 is trying to lock:
   ffff000800855898 (&port_lock_key){....}-{3:3}, at:
pl011_console_write+0x148/0x240
   other info that might help us debug this:
   context-{2:2}
   5 locks held by kworker/u8:0/9:
    #0: ffff00080032a138 ((wq_completion)eval_map_wq){+.+.}-{0:0}, at:
process_one_work+0x200/0x6b0
    #1: ffff80000807bde0
((work_completion)(&eval_map_work)){+.+.}-{0:0}, at:
process_one_work+0x200/0x6b0
    #2: ffff80000aa3db70 (trace_event_sem){+.+.}-{4:4}, at:
trace_event_eval_update+0x28/0x420
    #3: ffff80000a9afe58 (console_lock){+.+.}-{0:0}, at:
vprintk_emit+0x130/0x380
    #4: ffff80000a9aff78 (console_owner){-...}-{0:0}, at:
console_emit_next_record.constprop.0+0x128/0x338
   stack backtrace:
   CPU: 0 PID: 9 Comm: kworker/u8:0 Not tainted 6.0.0-rc7 #38
   Hardware name: Foundation-v8A (DT)
   Workqueue: eval_map_wq eval_map_work_func
   Call trace:
    dump_backtrace+0x114/0x120
    show_stack+0x20/0x58
    dump_stack_lvl+0x9c/0xd8
    dump_stack+0x18/0x34
    __lock_acquire+0x17cc/0x1920
    lock_acquire+0x138/0x3b8
    _raw_spin_lock+0x58/0x70
    pl011_console_write+0x148/0x240
    console_emit_next_record.constprop.0+0x194/0x338
    console_unlock+0x18c/0x208
    vprintk_emit+0x24c/0x380
    vprintk_default+0x40/0x50
    vprintk+0xd4/0xf0
    _printk+0x68/0x90
    arm64_pmu_brbe_probe+0x10c/0x128
    armv8pmu_brbe_probe+0x18/0x28
    arm_brbe_probe_cpu+0x44/0x58
    __flush_smp_call_function_queue+0x1d0/0x440
    generic_smp_call_function_single_interrupt+0x20/0x78
    ipi_handler+0x98/0x368
    handle_percpu_devid_irq+0xc0/0x3a8
    generic_handle_domain_irq+0x34/0x50
    gic_handle_irq+0x58/0x138
    call_on_irq_stack+0x2c/0x58
    do_interrupt_handler+0x88/0x90
    el1_interrupt+0x40/0x78
    el1h_64_irq_handler+0x18/0x28
    el1h_64_irq+0x64/0x68
    trace_event_eval_update+0x114/0x420
    eval_map_work_func+0x30/0x40
    process_one_work+0x298/0x6b0
    worker_thread+0x54/0x408
    kthread+0x118/0x128
    ret_from_fork+0x10/0x20
   brbe: implementation found on cpu 1
   brbe: implementation found on cpu 2
   brbe: implementation found on cpu 3

> +		if (err)
> +			return err;
> +	}
> +	return err;
> +}
> +
>  static void armpmu_free_irqs(struct arm_pmu *armpmu)
>  {
>  	int cpu;
> @@ -229,6 +259,10 @@ int arm_pmu_device_probe(struct platform_device *pdev,
>  	if (ret)
>  		goto out_free_irqs;
>  
> +	ret = armpmu_request_brbe(pmu);
> +	if (ret)
> +		goto out_free_irqs;
> +
>  	ret = armpmu_register(pmu);
>  	if (ret) {
>  		dev_err(dev, "failed to register PMU devices!\n");