linux-kernel - Re: [PATCH 3/3] blk-mq: Use llist_head for blk_cpu

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Message-ID: <20201028144453.GA18610@infradead.org>
Date:   Wed, 28 Oct 2020 14:44:53 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-block@...r.kernel.org, Christoph Hellwig <hch@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        David Runge <dave@...epmap.de>, linux-rt-users@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Daniel Wagner <dwagner@...e.de>
Subject: Re: [PATCH 3/3] blk-mq: Use llist_head for blk_cpu_done

On Wed, Oct 28, 2020 at 03:12:51PM +0100, Sebastian Andrzej Siewior wrote:
>  static int blk_softirq_cpu_dead(unsigned int cpu)
>  {
> -	/*
> -	 * If a CPU goes away, splice its entries to the current CPU
> -	 * and trigger a run of the softirq
> -	 */
> -	local_irq_disable();
> -	list_splice_init(&per_cpu(blk_cpu_done, cpu),
> -			 this_cpu_ptr(&blk_cpu_done));
> -	raise_softirq_irqoff(BLOCK_SOFTIRQ);
> -	local_irq_enable();
> -
> +	blk_complete_reqs(&per_cpu(blk_cpu_done, cpu));
>  	return 0;

How can this be preempted?  Can't we keep using this_cpu_ptr here?