[PATCH] NVMe: do not touch sq door bell if nvmeq has been suspended

nvme interrupt handler touches cq door bell, so actually before unmap it must be taken care of too. Currently it checks cq_vector >= 0 to avoid touching unmapped door bell. 

I think it is better to let queue_rq and interrupt handler use the same mechanism to detect unmap, by driver itself (e.g. cq_vector) or by block layer (e.g. a new API to guarantee no inflight IO under hw queue).


-----Original Message-----
From: Sagi Grimberg [mailto:sagig@dev.mellanox.co.il] 
Sent: Wednesday, February 3, 2016 1:20 AM
To: Keith Busch
Cc: Wenbo Wang; Jens Axboe; Wenbo Wang; Wenwei.Tao; linux-kernel at vger.kernel.org; linux-nvme at lists.infradead.org
Subject: Re: [PATCH] NVMe: do not touch sq door bell if nvmeq has been suspended

We free the transfer buffers when a command is cancelled. The 
controller, however, may still own the command and may try to write to 
them. We have to fence the controller off from being able to do that, 
so we can't cancel inflight commands while the PCI device is still bus master enabled.

In a perfect world, we could trust in disabling with NVMe registers, 
but sometimes we can't rely on that.

OK, I wasn't aware that we cannot rely on that.

So it looks like we cannot change the ordering. So this leaves us with the need to guarantee that no queue_rq is inflight before we unmap.