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

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Message-ID: <alpine.LNX.2.00.1505221700120.15930@localhost.lm.intel.com>
Date:	Fri, 22 May 2015 17:07:22 +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:
> On Fri, May 22, 2015 at 9:53 PM, Keith Busch <keith.busch@...el.com> wrote:
>> A memory barrier before incrementing the dev->queue_count (and assigning
>> the pointer in the array before that) should address this concern.
>
> Sure. mb() will solve the publisher side problem. RCU is wrapper around mb().
> However mb() doesn't solve the issue of q_lock variable getting
> fetched before if (!nvmeq) condition being executed, by value
> compilation optimizations in nvme_kthread().

Eh? The value of dev->queue_count prevents the thread's for-loop from
iterating that nvmeq before the q_lock is initialized.
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