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Date: Mon, 21 Aug 2017 14:07:37 +0200
From: Christoph Hellwig <hch@lst.de>
To: Marc Zyngier <marc.zyngier@arm.com>
Cc: YASUAKI ISHIMATSU <yasu.isimatu@gmail.com>, tglx@linutronix.de,
        axboe@kernel.dk, mpe@ellerman.id.au, keith.busch@intel.com,
        peterz@infradead.org, LKML <linux-kernel@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>
Subject: Re: system hung up when offlining CPUs
Message-ID: <20170821120737.GA11622@lst.de>
References: <c55a33b4-a886-8882-dd8d-5c488f94ee06@gmail.com> <20170809124213.0d9518bb@why.wild-wind.fr.eu.org> <cd524af7-1f20-1956-1e44-92a451053387@gmail.com> <c1c7e0d6-d908-b511-8418-bca288a0d20a@arm.com>
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Hi Marc,

in general the driver should know not to use the queue / irq,
as blk-mq will never schedule I/O to queues that have no online
cpus.

The real bugs seems to be that we're using affinity for a device
that only has one real queue (as the config queue should not
have affinity).  Let me dig into what's going on here with virtio.