[PATCH V2 0/4] nvme: fix two kinds of IO hang from removing NSs

[Ming Lei]

On Tue, Jun 27, 2023 at 11:21:36AM -0600, Keith Busch wrote:
> On Sun, Jun 25, 2023 at 08:26:48AM +0800, Ming Lei wrote:
> > Yeah, but you can't remove the gap at all with start_freeze, that said
> > the current code has to live with the situation of new mapping change
> > and old request with old mapping.
> > 
> > Actually I considered to handle this kind of situation before, one approach
> > is to reuse the bio steal logic taken in nvme mpath:
> > 
> > 1) for FS IO, re-submit bios, meantime free request
> > 
> > 2) for PT request, simply fail it
> > 
> > It could be a bit violent for 2) even though REQ_FAILFAST_DRIVER is
> > always set for PT request, but not see any better approach for handling
> > PT request.
> 
> I think that's acceptable for PT requests, or any request that doesn't
> have a bio. I tried something similiar a while back that was almost
> working, but I neither never posted it, or it's in that window when
> infradead lost all the emails. :(
> 
> Anyway, for the pci controller, I think I see the problem you're fixing.
> When reset_work fails, we used to do the mark dead + unquieces via
> "nvme_kill_queues()", which doesn't exist anymore, but I think your
> scenario worked back then. Currently a failed nvme_reset_work simply
> marks them dead without the unquiesce. Would it be enough to just bring
> that unqueisce behavior back?
> 
> ---
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index b027e5e3f4acb..8eaa954aa6ed4 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -2778,6 +2778,7 @@ static void nvme_reset_work(struct work_struct *work)
>  	nvme_change_ctrl_state(&dev->ctrl, NVME_CTRL_DELETING);
>  	nvme_dev_disable(dev, true);
>  	nvme_mark_namespaces_dead(&dev->ctrl);
> +	nvme_unquiesce_io_queues(&dev->ctrl);
>  	nvme_change_ctrl_state(&dev->ctrl, NVME_CTRL_DEAD);
>  }

That may not be enough:

- What if nvme_sysfs_delete() is called from sysfs before the 1st check in
nvme_reset_work()?

- What if one pending nvme_dev_disable()<-nvme_timeout() comes after
the added nvme_unquiesce_io_queues() returns?


Thanks,
Ming