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

[Nilay Shroff <nilay@linux.ibm.com>]

On 1/12/26 1:44 PM, Daniel Wagner wrote:
> 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/
> 
I have tested this (and I believe John as well) and this seems tobe working good. From my code walk through, the controller state
transition RESETTING -> CONNECTING -> LIVE looks good to me, so I'll
send out a formal patch for review. 

Thanks,
--Nilay