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

[Dan Williams]

On Fri, Nov 18, 2016 at 1:00 AM, John Garry <john.garry@xxxxxxxxxx> wrote:
> On 18/11/2016 01:53, Dan Williams wrote:
>>
>> On Thu, Nov 17, 2016 at 7:23 AM, John Garry <john.garry@xxxxxxxxxx> 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)