linux-kernel - Re: [PATCH 0/4] Rework NVMe abort handling

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Date:   Thu, 19 Jul 2018 16:50:05 +0200
From:   Christoph Hellwig <hch@....de>
To:     Johannes Thumshirn <jthumshirn@...e.de>
Cc:     Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>,
        Keith Busch <keith.busch@...el.com>,
        James Smart <james.smart@...adcom.com>,
        Hannes Reinecke <hare@...e.de>, Ewan Milne <emilne@...hat.com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Linux NVMe Mailinglist <linux-nvme@...ts.infradead.org>,
        Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/4] Rework NVMe abort handling

On Thu, Jul 19, 2018 at 04:35:34PM +0200, Johannes Thumshirn wrote:
> > No with the the code following what we have in PCIe that just means
> > we'll eventually controller reset after the I/O command times out
> > the second time as we still won't have seen a completion for it.
> 
> Exactly that was my intention.

Which means the only thing you do for your use case is to delay
recovery even further.

> OK, let me see where I'm stuck here. We're issuing a command, it gets
> lost due to $REASON and I'm aborting it. The upper layers then
> eventually retry the command and it arrives at the target side. But so
> does the old command as well and we have a duplicate. Correct?

The upper layer is only going to retry after tearing down the transport
connection.  And a tear down of the connection MUST clear all pending
commands on the way.  If it doesn't we are in deep, deep trouble.

A NVMe abort has no chance of clearing things at the transport layer.