linux-kernel - Re: [PATCH 1/4] softirq: implement IRQ flood detection mechanism

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.21.1908271633450.1939@nanos.tec.linutronix.de>
Date:   Tue, 27 Aug 2019 16:42:02 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ming Lei <ming.lei@...hat.com>
cc:     linux-kernel@...r.kernel.org, Long Li <longli@...rosoft.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Keith Busch <keith.busch@...el.com>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        John Garry <john.garry@...wei.com>,
        Hannes Reinecke <hare@...e.com>,
        linux-nvme@...ts.infradead.org, linux-scsi@...r.kernel.org
Subject: Re: [PATCH 1/4] softirq: implement IRQ flood detection mechanism

On Tue, 27 Aug 2019, Ming Lei wrote:
> +/*
> + * Update average irq interval with the Exponential Weighted Moving
> + * Average(EWMA)
> + */
> +static void irq_update_interval(void)
> +{
> +#define IRQ_INTERVAL_EWMA_WEIGHT	128
> +#define IRQ_INTERVAL_EWMA_PREV_FACTOR	127
> +#define IRQ_INTERVAL_EWMA_CURR_FACTOR	(IRQ_INTERVAL_EWMA_WEIGHT - \
> +		IRQ_INTERVAL_EWMA_PREV_FACTOR)

Please do not stick defines into a function body. That's horrible.

> +
> +	int cpu = raw_smp_processor_id();
> +	struct irq_interval *inter = per_cpu_ptr(&avg_irq_interval, cpu);
> +	u64 delta = sched_clock_cpu(cpu) - inter->last_irq_end;

Why are you doing that raw_smp_processor_id() dance? The call site has
interrupts and preemption disabled.

Also how is that supposed to work when sched_clock is jiffies based?

> +	inter->avg = (inter->avg * IRQ_INTERVAL_EWMA_PREV_FACTOR +
> +		delta * IRQ_INTERVAL_EWMA_CURR_FACTOR) /
> +		IRQ_INTERVAL_EWMA_WEIGHT;

We definitely are not going to have a 64bit multiplication and division on
every interrupt. Asided of that this breaks 32bit builds all over the place.

Thanks,

	tglx