[PATCH 2/2] nvme: don't do scan work if io queue count is zero

[Sagi Grimberg]

> On Tue, Aug 03, 2021 at 05:06:30PM +0800, Ruozhu Li wrote:
>> kernel panic when try to rescan ns when io queue count is zero.Because
>> kernel BUG_ON when hctx_idx is greater than ctrl->queue_count.
>> --
>> nvme_rdma_init_hctx+0x58/0x60 [nvme_rdma]
>> blk_mq_realloc_hw_ctxs+0x140/0x4c0
>> blk_mq_init_allocated_queue+0x130/0x410
>> blk_mq_init_queue+0x40/0x88
>> nvme_validate_ns+0xb8/0x740
>> nvme_scan_work+0x29c/0x460
>> process_one_work+0x1f8/0x490
>> worker_thread+0x50/0x4b8
>> kthread+0x134/0x138
>> ret_from_fork+0x10/0x18
>> --
>> Defence it by not allowing rescan ns when io queue count is zero.
>>
>> Signed-off-by: Ruozhu Li <liruozhu at huawei.com>
>> ---
>>   drivers/nvme/host/core.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
>> index dfd9dec0c1f6..d9f837eb3e26 100644
>> --- a/drivers/nvme/host/core.c
>> +++ b/drivers/nvme/host/core.c
>> @@ -141,7 +141,8 @@ void nvme_queue_scan(struct nvme_ctrl *ctrl)
>>   	/*
>>   	 * Only new queue scan work when admin and IO queues are both alive
>>   	 */
>> -	if (ctrl->state == NVME_CTRL_LIVE && ctrl->tagset)
>> +	if (ctrl->state == NVME_CTRL_LIVE &&
>> +	    ctrl->tagset && ctrl->queue_count > 1)
> 
> Why is the transport driver leaving an unusable tagset allocated when
> there are no IO queues to support it? I think it should free the tagset
> in that case. At least that's what pci does.

We can't release the tagset as that will fail I/O (which is probably
fine for mpath) but for non-mpath we want I/O to block.