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

[John Garry]

On 11/11/2016 08:12, wangyijing wrote:
> > They're not the same. I don't see how your solution properly deals with remote sas_port deletion.
> >
> > When we unplug a device connected to an expander, can't the sas_port be deleted twice, in sas_unregister_devs_sas_addr() from domain revalidation and also now in sas_destruct_devices()? I think that this gives a NULL dereference.
> > And we still get the WARN as the sas_port has still been deleted before the device.
> >
> > In my solution, we should always delete the sas_port after the attached device.
> >
> > > > i.e. it moves the port destruction to the workqueue and still suffers
> > > > from the flutter problem:
> > > >
> > > > http://marc.info/?l=linux-scsi&m=143801026028006&w=2
> > > > http://marc.info/?l=linux-scsi&m=143801971131073&w=2
> > > >
> > > > Perhaps we instead need to quiet this warning?
> > > >
> > > > http://marc.info/?l=linux-scsi&m=143802229932175&w=2
> >
> > 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.

> 2. hot-add and hot-remove work events may process out of order;
> 3. in some extreme cases, libsas may miss some events, if the same event is still pending in workqueue.

Can you tell me how to recreate #2 and #3?

> It's a complex issue, we posted two patches, try to fix these issues, but now few people are interested in it  :(

IIRC, you sent as RFC and got a "reviewed-by" from Hannes, so I'm not 
sure what else you want. BTW, I thought that the changes were quite drastic.

John

> > > Alternatively we need a mechanism to cancel in-flight port shutdown
> > > requests when we start re-attaching devices before queued port
> > > destruction events have run.
> > >
> > > .
> >
> >
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