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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Yunfeng Ye <yeyunfeng@huawei.com>
Cc:     linux-kernel@vger.kernel.org, Shiyuan Hu <hushiyuan@huawei.com>,
        Hewenliang <hewenliang4@huawei.com>
Subject: Re: [PATCH] genirq/proc: Show percpu irq affinity
In-Reply-To: <fcb0ae13-95b0-37d3-c1f9-44727e0f2ce8@huawei.com>
References: <fcb0ae13-95b0-37d3-c1f9-44727e0f2ce8@huawei.com>
Date:   Thu, 13 Aug 2020 10:27:53 +0200
Message-ID: <874kp754s6.fsf@nanos.tec.linutronix.de>
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
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Yunfeng Ye <yeyunfeng@huawei.com> writes:

> When the "affinity=" cmdline parameter is configured,

There is no such parameter.

> the interrupt affinity displayed in the proc directory does not match
> with that of the the percu interrupt, and the percu interrupt uses
> desc->percu_affinity.

And when the non-existing parameter is not on the command line then
irq->affinity is showing the correct value magically?

Definitely not: It's unconditionally showing irq->affinity and that is
pretty unlikely to match irq->percpu_affinity in any case.

> diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
> index 32c071d7bc03..b9d0fa87b4b4 100644
> --- a/kernel/irq/proc.c
> +++ b/kernel/irq/proc.c
> @@ -52,6 +52,8 @@ static int show_irq_affinity(int type, struct seq_file *m)
>  	case AFFINITY:
>  	case AFFINITY_LIST:
>  		mask = desc->irq_common_data.affinity;
> +		if (irqd_is_per_cpu(&desc->irq_data))
> +			mask = desc->percpu_affinity;

This breaks all architecture which mark interrupts as per CPU without
using the partition mechanism resulting in a NULL pointer dereference.

Thanks,

        tglx