linux-kernel - Re: [PATCH 1/2] nvme: only allow entering LIVE from CONNECTING state

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Message-ID: <d8512cdc-bdcd-44ff-a56a-974b4464a7a5@flourine.local>
Date: Mon, 12 Jan 2026 09:14:33 +0100
From: Daniel Wagner <dwagner@...e.de>
To: Nilay Shroff <nilay@...ux.ibm.com>
Cc: John Meneghini <jmeneghi@...hat.com>, Daniel Wagner <wagi@...nel.org>, 
	Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>, 
	Sagi Grimberg <sagi@...mberg.me>, James Smart <james.smart@...adcom.com>, 
	Hannes Reinecke <hare@...e.de>, Shinichiro Kawasaki <shinichiro.kawasaki@....com>, 
	Wen Xiong <wenxiong@...ux.ibm.com>, Narayana Murty N <nnmlinux@...ux.ibm.com>, 
	linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org, Ewan Milne <emilne@...hat.com>, 
	Maurizio Lombardi <mlombard@...hat.com>
Subject: Re: [PATCH 1/2] nvme: only allow entering LIVE from CONNECTING state

Hi Nilay,

On Sun, Jan 11, 2026 at 03:03:43PM +0530, Nilay Shroff wrote:
> This was broken because with this commit d2fe192348f9 (“nvme: only allow entering LIVE
> from CONNECTING state”) now we don't allow changing controller state from 
> RESETTING -> LIVE. I saw we also had similar state change issue with firmware activation 
> code which was fixed by explicitly transitioning the controller state through RESETTING ->
> CONNECTING -> LIVE. We may employ the similar solution here for subsystem reset case as well. 
> 
> Currently, the NVMe PCIe subsystem reset code performs the following steps:
> 
> 1. Sets the controller state to RESETTING
> 2. Writes the subsystem reset command to the NSSR register
> 3. Attempts to transition the controller state directly to LIVE
> 
> This effectively bypasses the CONNECTING state. The transition to LIVE is artificial but
> intentional, since writing to the NSSR register causes the loss of communication with the
> NVMe adapter and the controller must be marked LIVE so that any in-flight I/O at the time the
> subsystem reset is issued, or an explicit MMIO read, can trigger EEH recovery and ultimately
> restore communication link between the NVMe adapter and the system.
> 
> With the stricter state transition rules introduced by commit d2fe192348f9 (“nvme: only allow
> entering LIVE from CONNECTING state”), the direct transition from RESETTING -> LIVE is no longer
> permitted, rendering the current logic ineffective.
> 
> Taking a cue from the firmware activation fix, it seems reasonable to explicitly transition
> the controller state through CONNECTING in the subsystem reset path as well. So how about making
> the following change to fix this? 
> 
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 0e4caeab739c..3027bba232de 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -1532,7 +1532,10 @@ static int nvme_pci_subsystem_reset(struct nvme_ctrl *ctrl)
>         }
>  
>         writel(NVME_SUBSYS_RESET, dev->bar + NVME_REG_NSSR);
> -       nvme_change_ctrl_state(ctrl, NVME_CTRL_LIVE);
> +
> +       if (!nvme_change_ctrl_state(ctrl, NVME_CTRL_CONNECTING) ||
> +           !nvme_change_ctrl_state(ctrl, NVME_CTRL_LIVE))
> +               goto unlock;
>  
>         /*
>          * Read controller status to flush the previous write and trigger a

This seems to be similar to case where the firmware update got stuck [1].

  650415fca0a9 ("nvme: unblock ctrl state transition for firmware update")

>From my understanding this should work, but it's probably better to
double check that this doesn't violate any assumptions.

[1] https://lore.kernel.org/all/aBJJQoOBhaXj7P36@kbusch-mbp/

Thanks,
Daniel