linux-kernel - Re: [PATCH] NVMe: Avoid interrupt disable during queue init.

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Date:	Fri, 22 May 2015 16:23:30 +0000 (UTC)
From:	Keith Busch <keith.busch@...el.com>
To:	Parav Pandit <parav.pandit@...gotech.com>
cc:	Keith Busch <keith.busch@...el.com>,
	linux-nvme@...ts.infradead.org,
	Matthew Wilcox <willy@...ux.intel.com>,
	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] NVMe: Avoid interrupt disable during queue init.

On Fri, 22 May 2015, Parav Pandit wrote:
> During normal positive path probe,
> (a) device is added to dev_list in nvme_dev_start()
> (b) nvme_kthread got created, which will eventually refers to
> dev->queues[qid] to check for NULL.
> (c) dev_start() worker thread has started probing device and creating
> the queue using nvme_alloc_queue
> This is is assigning the dev->queue[qid] new pointer.
> If this is done out of order, nvme_kthread will pickup uninitialized
> q_lock, cq_phase, q_db.

A memory barrier before incrementing the dev->queue_count (and assigning
the pointer in the array before that) should address this concern.

> Other thoughts to not create nvme_kthread until all the queues are active.

No good, we want to poll during queue creation to detect controller
errors and broken interrupts.
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