Re: [PATCH V5 0/9] nvme: pci: fix & improve timeout handling

["jianchao.wang" <jianchao.w.wang@oracle.com>]

Hi ming

On 05/14/2018 05:38 PM, Ming Lei wrote:
>> Here is the deadlock scenario.
>>
>> nvme_eh_work // EH0
>>   -> nvme_reset_dev //hold reset_lock
>>     -> nvme_setup_io_queues
>>       -> nvme_create_io_queues
>>         -> nvme_create_queue
>>           -> set nvmeq->cq_vector
>>           -> adapter_alloc_cq
>>           -> adapter_alloc_sq
>>              irq has not been requested
>>              io timeout 
>>                                     nvme_eh_work //EH1
>>                                       -> nvme_dev_disable
>>                                         -> quiesce the adminq //----> here !
>>                                         -> nvme_suspend_queue
>>                                           print out warning Trying to free already-free IRQ 133
>>                                         -> nvme_cancel_request // complete the timeout admin request
>>                                       -> require reset_lock
>>           -> adapter_delete_cq
> If the admin IO submitted in adapter_alloc_sq() is timed out,
> nvme_dev_disable() in EH1 will complete it which is set as REQ_FAILFAST_DRIVER,
> then adapter_alloc_sq() should return error, and the whole reset in EH0
> should have been terminated immediately.

Please refer to the following segment:

static int nvme_create_queue(struct nvme_queue *nvmeq, int qid)
{
	struct nvme_dev *dev = nvmeq->dev;
	int result;
...
	nvmeq->cq_vector = dev->num_vecs == 1 ? 0 : qid;
	result = adapter_alloc_cq(dev, qid, nvmeq);
	if (result < 0)
		goto release_vector;

	result = adapter_alloc_sq(dev, qid, nvmeq);   // if timeout and failed here
	if (result < 0)
		goto release_cq;

	nvme_init_queue(nvmeq, qid);
	result = queue_request_irq(nvmeq);
	if (result < 0)
		goto release_sq;

	return result;

 release_sq:
	dev->online_queues--;
	adapter_delete_sq(dev, qid);
 release_cq:                                        // we will be here !
	adapter_delete_cq(dev, qid);                // another cq delete admin command will be sent out.
 release_vector:
	nvmeq->cq_vector = -1;
	return result;
}


> 
> I guess the issue should be that nvme_create_io_queues() ignores the failure.
> 
> Could you dump the stack trace of EH0 reset task? So that we may see
> where EH0 reset kthread hangs.

root@will-ThinkCentre-M910s:/home/will/Desktop# cat /proc/2273/stack 
[<0>] blk_execute_rq+0xf7/0x150
[<0>] __nvme_submit_sync_cmd+0x94/0x110
[<0>] nvme_submit_sync_cmd+0x1b/0x20
[<0>] adapter_delete_queue+0xad/0xf0
[<0>] nvme_reset_dev+0x1b67/0x2450
[<0>] nvme_eh_work+0x19c/0x4b0
[<0>] process_one_work+0x3ca/0xaa0
[<0>] worker_thread+0x89/0x6c0
[<0>] kthread+0x18d/0x1e0
[<0>] ret_from_fork+0x24/0x30
[<0>] 0xffffffffffffffff
root@will-ThinkCentre-M910s:/home/will/Desktop# cat /proc/2275/stack 
[<0>] nvme_eh_work+0x11a/0x4b0
[<0>] process_one_work+0x3ca/0xaa0
[<0>] worker_thread+0x89/0x6c0
[<0>] kthread+0x18d/0x1e0
[<0>] ret_from_fork+0x24/0x30
[<0>] 0xffffffffffffffff

> 
>>             -> adapter_delete_queue // submit to the adminq which has been quiesced.
>>               -> nvme_submit_sync_cmd
>>                 -> blk_execute_rq
>>                   -> wait_for_completion_io_timeout
>>                   hang_check is true, so there is no hung task warning for this context
>>
>> EH0 submit cq delete admin command, but it will never be completed or timed out, because the admin request queue has
>> been quiesced, so the reset_lock cannot be released, and EH1 cannot get reset_lock and make things forward.
> The nvme_dev_disable() in outer EH(EH1 in above log) will complete all
> admin command, which won't be retried because it is set as
> REQ_FAILFAST_DRIVER, so nvme_cancel_request() will complete it in
> nvme_dev_disable().

This cq delete admin command is sent out after EH 1 nvme_dev_disable completed and failed the
previous timeout sq alloc admin command. please refer to the code segment above.

Thanks
jianchao