linux-kernel - Re: [PATCH 0/2] genirq/affinity: try to make sure online CPU is assgined to irq vector

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Date:   Tue, 16 Jan 2018 12:25:19 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ming Lei <ming.lei@...hat.com>
cc:     Christoph Hellwig <hch@...radead.org>, Jens Axboe <axboe@...com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Laurence Oberman <loberman@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>
Subject: Re: [PATCH 0/2] genirq/affinity: try to make sure online CPU is
 assgined to irq vector

On Tue, 16 Jan 2018, Ming Lei wrote:

> On Mon, Jan 15, 2018 at 09:40:36AM -0800, Christoph Hellwig wrote:
> > On Tue, Jan 16, 2018 at 12:03:43AM +0800, Ming Lei wrote:
> > > Hi,
> > > 
> > > These two patches fixes IO hang issue reported by Laurence.
> > > 
> > > 84676c1f21 ("genirq/affinity: assign vectors to all possible CPUs")
> > > may cause one irq vector assigned to all offline CPUs, then this vector
> > > can't handle irq any more.
> > 
> > Well, that very much was the intention of managed interrupts.  Why
> > does the device raise an interrupt for a queue that has no online
> > cpu assigned to it?
> 
> It is because of irq_create_affinity_masks().

That still does not answer the question. If the interrupt for a queue is
assigned to an offline CPU, then the queue should not be used and never
raise an interrupt. That's how managed interrupts have been designed.

Thanks,

	tglx