linux-kernel - Re: [PATCH V2 0/6]nvme-pci: fixes on nvme_timeout and nvme_dev

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Date:   Fri, 9 Feb 2018 09:50:58 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>
Cc:     axboe@...com, hch@....de, linux-nvme@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 0/6]nvme-pci: fixes on nvme_timeout and
 nvme_dev_disable

Hi Keith and Sagi

Many thanks for your kindly response.
That's really appreciated.

On 02/09/2018 01:56 AM, Keith Busch wrote:
> On Thu, Feb 08, 2018 at 05:56:49PM +0200, Sagi Grimberg wrote:
>> Given the discussion on this set, you plan to respin again
>> for 4.16?
> 
> With the exception of maybe patch 1, this needs more consideration than
> I'd feel okay with for the 4.16 release.
> 
Currently, one of the block is the nvme_wait_freeze in nvme_reset_work.
This cause some issues when I test this patchset yesterday.
As I posted on the V1 patchset mail thread:

if we set NVME_REQ_CANCELLED and return BLK_EH_HANDLED as the RESETTING case,
nvme_reset_work will hang forever, because no one could complete the entered requests.

if we invoke nvme_reset_ctrl after modify the state machine to be able to change to RESETTING
to RECONNECTING and queue reset_work, we still cannot move things forward, because the reset_work
is being executed.

if we use nvme_wait_freeze_timeout in nvme_reset_work, unfreeze and return if expires. But the 
timeout value is tricky..

And actually, one of the possible solution to fix this cleanly is blk_set_preempt_only.
It is a lightweight way to gate the new bios out of generic_make_request.

Looking forward your advice on this.
And many thanks for your precious time on this.

Sincerely
Thanks
Jianchao