In most cases, rcu read lock is just a preempt_disable, which is what get_cpu does. I don't see any risk.

-----Original Message-----
From: Keith Busch [mailto:keith.busch@intel.com] 
Sent: Monday, February 8, 2016 11:02 PM
To: Wenbo Wang
Cc: Jens Axboe; Wenbo Wang; linux-kernel at vger.kernel.org; linux-nvme at lists.infradead.org; Wenwei.Tao
Subject: Re: [PATCH] NVMe: do not touch sq door bell if nvmeq has been suspended

On Sat, Feb 06, 2016@02:32:24PM +0000, Wenbo Wang wrote:

Keith,

Is the following solution OK?
synchronize_rcu guarantee that no queue_rq is running concurrently with device disable code. Together with your another patch (adding blk_sync_queue), both sync/async path shall be handled correctly.

Do you think synchronize_rcu shall be added to blk_sync_queue?

I was nearly going to suggest the same last week, but it feels wrong since no one takes rcu_read_lock in the path we're trying to sychronoize. Is this safe if the task is interrupted?