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

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Date:   Fri, 18 Nov 2016 11:08:04 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     John Garry <john.garry@...wei.com>
Cc:     jejb@...ux.vnet.ibm.com,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        wangyijing <wangyijing@...wei.com>,
        linux-scsi <linux-scsi@...r.kernel.org>,
        John Garry <john.garry2@...l.dcu.ie>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linuxarm@...wei.com, lindar_liu@...sh.com,
        Tejun Heo <tj@...nel.org>,
        Jinpu Wang <jinpu.wang@...fitbricks.com>
Subject: Re: [RFC PATCH] scsi: libsas: fix WARN on device removal

On Fri, Nov 18, 2016 at 1:00 AM, John Garry <john.garry@...wei.com> wrote:
> On 18/11/2016 01:53, Dan Williams wrote:
>>
>> On Thu, Nov 17, 2016 at 7:23 AM, John Garry <john.garry@...wei.com> wrote:
>>>
>>> On 11/11/2016 08:49, wangyijing wrote:
>>>>>>>
>>>>>>>
>>>>>>> I have not seen the flutter issue. I am just trying to solve the
>>>>>>> horrible WARN dump.
>>>>>>> However I do understand that there may be a issue related to how we
>>>>>>> queue the events; there was a recent attempt to fix this, but it came
>>>>>>> to
>>>>>>> nothing:
>>>>>>> https://www.spinics.net/lists/linux-scsi/msg99991.html
>>>>>>
>>>>>>
>>>>>>
>>>>>> We found libsas hotplug several problems:
>>>>>> 1. sysfs warning calltrace(like the case you found);
>>>>>
>>>>>
>>>>>
>>>>> Maybe you can then review my patch.
>>>>
>>>>
>>>>
>>>> I did it, I think your solution to fix the sysfs calltrace issue is ok,
>>>> and what I worried about is we still need to fix
>>>> the rest issues. So it's better if we could fix all issues one time.
>>>>
>>>
>>> @Maintainers, would you be willing to accept this patch as an interim fix
>>> for the dastardly WARN while we try to fix the flutter issue?
>>
>>
>> To me this adds a bug to quiet a benign, albeit noisy, warning.
>>
>
> What is the bug which is being added?

The bug where we queue a port teardown, but see a port formation event
in the meantime.

> 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?

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)