linux-kernel - Re: [PATCH v11 2/8] hwtracing: hisi_ptt: Add trace function support for HiSilicon PCIe Tune and Trace device

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Date:   Fri, 29 Jul 2022 11:05:34 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Yicong Yang <yangyicong@...wei.com>
Cc:     yangyicong@...ilicon.com, alexander.shishkin@...ux.intel.com,
        leo.yan@...aro.org, james.clark@....com, will@...nel.org,
        robin.murphy@....com, acme@...nel.org, peterz@...radead.org,
        corbet@....net, mathieu.poirier@...aro.org, mark.rutland@....com,
        jonathan.cameron@...wei.com, john.garry@...wei.com,
        helgaas@...nel.org, lorenzo.pieralisi@....com,
        suzuki.poulose@....com, joro@...tes.org,
        shameerali.kolothum.thodi@...wei.com, mingo@...hat.com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pci@...r.kernel.org, linux-perf-users@...r.kernel.org,
        iommu@...ts.linux-foundation.org, iommu@...ts.linux.dev,
        linux-doc@...r.kernel.org, prime.zeng@...wei.com,
        liuqi115@...wei.com, zhangshaokun@...ilicon.com,
        linuxarm@...wei.com, bagasdotme@...il.com
Subject: Re: [PATCH v11 2/8] hwtracing: hisi_ptt: Add trace function support
 for HiSilicon PCIe Tune and Trace device

On Fri, Jul 29, 2022 at 03:29:14PM +0800, Yicong Yang wrote:
> >> +	/*
> >> +	 * Handle the interrupt on the same cpu which starts the trace to avoid
> >> +	 * context mismatch. Otherwise we'll trigger the WARN from the perf
> >> +	 * core in event_function_local().
> >> +	 */
> >> +	WARN_ON(irq_set_affinity(pci_irq_vector(hisi_ptt->pdev, HISI_PTT_TRACE_DMA_IRQ),
> >> +				 cpumask_of(cpu)));
> > 
> > If this hits, you just crashed the machine :(
> > 
> 
> We'll likely to have a calltrace here without crash the machine and reboot in
> most time, unless user has set panic_on_warn.

Again, please do not use WARN_ON for this, please read:
	https://elixir.bootlin.com/linux/v5.19-rc8/source/include/asm-generic/bug.h#L74

If you want a traceback (what would you do with that?), then call the
function to give you that.  Don't crash people's boxes.

> > Please properly recover from errors if you hit them, like this.  Don't
> > just give up and throw a message to userspace and watch the machine
> > reboot with all data lost.
> > 
> > Same for the other WARN_ON() instances here.  Handle the error and
> > report it properly up the call chain.
> > 
> 
> The driver use WARN_ON() in two places, once in pmu::start() and another in cpu teardown's
> callback, both when the irq_set_affinity() failed. This is common to behave so when driver
> fails to set irq affinity in pmu::start() and cpu_teardown():

Don't repeat broken patterns please.

> yangyicong@...ntu:~/mainline_linux/linux/drivers$ grep -rn WARN_ON ./ | grep irq_set_affinity
> ./perf/arm_smmuv3_pmu.c:649:    WARN_ON(irq_set_affinity(smmu_pmu->irq, cpumask_of(target)));
> ./perf/arm_smmuv3_pmu.c:895:    WARN_ON(irq_set_affinity(smmu_pmu->irq, cpumask_of(smmu_pmu->on_cpu)));
> ./perf/arm-ccn.c:1214:          WARN_ON(irq_set_affinity(ccn->irq, cpumask_of(dt->cpu)));
> ./perf/qcom_l2_pmu.c:796:       WARN_ON(irq_set_affinity(cluster->irq, cpumask_of(cpu)));
> ./perf/qcom_l2_pmu.c:834:       WARN_ON(irq_set_affinity(cluster->irq, cpumask_of(target)));
> ./perf/arm_dmc620_pmu.c:624:    WARN_ON(irq_set_affinity(irq->irq_num, cpumask_of(target)));
> ./perf/fsl_imx8_ddr_perf.c:674: WARN_ON(irq_set_affinity(pmu->irq, cpumask_of(pmu->cpu)));
> ./perf/xgene_pmu.c:1793:        WARN_ON(irq_set_affinity(xgene_pmu->irq, &xgene_pmu->cpu));
> ./perf/xgene_pmu.c:1826:        WARN_ON(irq_set_affinity(xgene_pmu->irq, &xgene_pmu->cpu));
> ./perf/hisilicon/hisi_pcie_pmu.c:658:           WARN_ON(irq_set_affinity(pcie_pmu->irq, cpumask_of(cpu)));
> ./perf/hisilicon/hisi_pcie_pmu.c:684:   WARN_ON(irq_set_affinity(pcie_pmu->irq, cpumask_of(target)));
> ./perf/hisilicon/hisi_uncore_pmu.c:495: WARN_ON(irq_set_affinity(hisi_pmu->irq, cpumask_of(cpu)));
> ./perf/hisilicon/hisi_uncore_pmu.c:528: WARN_ON(irq_set_affinity(hisi_pmu->irq, cpumask_of(target)));

Great, you can fix all of these up as well any time :)

thanks,

greg k-h