Re: [RFC PATCH] scsi: libsas: fix WARN on device removal

From: wangyijing <wangyijing@huawei.com>
To: John Garry <john.garry@huawei.com>,
	Dan Williams <dan.j.williams@intel.com>
Cc: <jejb@linux.vnet.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	linux-scsi <linux-scsi@vger.kernel.org>,
	"John Garry" <john.garry2@mail.dcu.ie>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	<linuxarm@huawei.com>, <lindar_liu@usish.com>,
	Tejun Heo <tj@kernel.org>,
	Jinpu Wang <jinpu.wang@profitbricks.com>
Subject: Re: [RFC PATCH] scsi: libsas: fix WARN on device removal
Date: Wed, 23 Nov 2016 09:07:32 +0800	[thread overview]
Message-ID: <5834EBD4.5010104@huawei.com> (raw)
In-Reply-To: <96fb83c2-ef02-181c-b27d-bb4c3dbc8194@huawei.com>

>>
>> The events are not lost.
> 
> In sas_queue_event(), if there is a particular event pending for a port/PHY, we cannot queue further same event types for that port/PHY. I think my colleagues found issue where we try to enqueue multiple complementary events.

Yes， we found this issue in our local tests.

> 
>> The new problem this patch introduces is
>> delaying sas port deletion where it was previously immediate.  So now
>> we can get into a situation where the port has gone down and can start
>> processing a port up event before the previous deletion work has run.
>>
>>>>
>>>>> And it's a very noisy warning, as in 6K lines on the console when an
>>>>> expander is unplugged.
>>>>
>>>>
>>>> Does something like this modulate the failure?
>>
>> I'm curious if we simply need to fix the double deletion of the
>> sas_port bsg queue, could you try the changes below?
>>
> 
> No, I just tested it on a root port and we get the same WARN.
> 
>>>>
>>>> diff --git a/drivers/scsi/scsi_transport_sas.c
>>>> b/drivers/scsi/scsi_transport_sas.c            index
>>>> 60b651bfaa01..11401e5c88ba 100644
>>>>                  --- a/drivers/scsi/scsi_transport_sas.c
>>>> +++ b/drivers/scsi/scsi_transport_sas.c
>>>> @@ -262,9 +262,10 @@ static void sas_bsg_remove(struct Scsi_Host
>>>> *shost, struct sas_rphy *rphy
>>>>  {
>>>>         struct request_queue *q;
>>>>
>>>> -       if (rphy)
>>>> +       if (rphy) {
>>>>                 q = rphy->q;
>>>> -       else
>>>> +               rphy->q = NULL;
>>>> +       } else
>>>>                 q = to_sas_host_attrs(shost)->q;
>>>>
>>>>         if (!q)
>>>>
>>>> .
>>>>
>>>
>>>
>>
>> .
>>
> 
> 
> 
> .
> 