Subject: Re: nvme-pci: NULL pointer dereference in nvme_dev_disable() on linux-next

From: Gerd Bayer <[email-masked]>
Date: Tue, 08 Nov 2022 18:11:01 +0100

Hi Christoph,

with your minimal fix

On Tue, 2022-11-08 at 08:48 +0100, Christoph Hellwig wrote:
> Below is the minimal fix.  I'll see if I sort out the mess that is
> probe/reset failure vs ->remove a bit better, though.
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index f94b05c585cbc..577bacdcfee08 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -5160,6 +5160,8 @@ EXPORT_SYMBOL_GPL(nvme_start_freeze);
>  
>  void nvme_stop_queues(struct nvme_ctrl *ctrl)
>  {
> +	if (!ctrl->tagset)
> +		return;
>  	if (!test_and_set_bit(NVME_CTRL_STOPPED, &ctrl->flags))
>  		blk_mq_quiesce_tagset(ctrl->tagset);
>  	else
> @@ -5169,6 +5171,8 @@ EXPORT_SYMBOL_GPL(nvme_stop_queues);
>  
>  void nvme_start_queues(struct nvme_ctrl *ctrl)
>  {
> +	if (!ctrl->tagset)
> +		return;
>  	if (test_and_clear_bit(NVME_CTRL_STOPPED, &ctrl->flags))
>  		blk_mq_unquiesce_tagset(ctrl->tagset);
>  }

on next-20221108 the kernel does not crash any
more when I run the short test-script.

dmesg shows:
Nov 08 17:38:51 a46lp24.lnxne.boe kernel: nvme nvme0: pci function 0004:00:00.0
Nov 08 17:38:51 a46lp24.lnxne.boe kernel:
nvme nvme0: failed to mark controller CONNECTING
Nov 08 17:38:51 a46lp24.lnxne.boe kernel: nvme nvme0: Removing after
probe failure status: -16
Nov 08 17:38:52 a46lp24.lnxne.boe kernel: pci 0004:00:00.0: Removing from iommu group 0

while kernel remains up.
I can even do 
- rescan on the pci bus (to bring back the nvme drive), and
- run the test script
multiple times.

So from my point of view this band-aid is valuable to be incorporated while the larger 
overhaul in

https://lore.kernel.org/linux-nvme/[email-masked]/
is out for review and test.

Feel free to add my
Tested-by: Gerd Bayer <[email-masked]>

Thank you,
Gerd Bayer