linux-kernel - Re: [Bug Report] nvme connect deadlock in allocating tag

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Message-ID: <d206c1d0-5935-476e-be19-9bec537af1b8@grimberg.me>
Date: Sun, 28 Apr 2024 12:30:30 +0300
From: Sagi Grimberg <sagi@...mberg.me>
To: Wangbing Kuang <wangbing.kuang@...pee.com>
Cc: james.smart@...adcom.com, kbusch@...nel.org, axboe@...com, hch@....de,
 linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
 chunguang.xu@...pee.com
Subject: Re: [Bug Report] nvme connect deadlock in allocating tag



On 28/04/2024 12:16, Wangbing Kuang wrote:
> "The error_recovery work should unquiesce the admin_q, which should fail
> fast all pending admin commands,
> so it is unclear to me how the connect process gets stuck."
> I think the reason is: the command can be unquiesce but the tag cannot be
> return until command success.

The error recovery also cancels all pending requests. See 
nvme_cancel_admin_tagset

>
> "What is step (2) - make nvme io timeout to recover the connection?"
> I use spdk-nvmf-target for backend.  It is easy to set read/write
> nvmf-target io  hang and unhang.  So I just set the io hang for over 30
> seconds, then trigger linux-nvmf-host trigger io timeout event. then io
> timeout will trigger connection recover.
> by the way, I use multipath=0

Interesting, does this happen with multipath=Y ?
I didn't expect people to be using multipath=0 for fabrics in the past few
years.

>
> "Is this reproducing with upstream nvme? or is this some distro kernel
> where this happens?"
> it is reproduced in a kernel based from v5.15, but I think this is common
> error.

It would be beneficial to verify this.