On Thu, Aug 11, 2016 at 08:09:35AM -0700, James Bottomley wrote:
> On Thu, 2016-08-11 at 09:59 +0200, Johannes Thumshirn wrote:
> > Since commit 3f8d6f2a0 ('ses: fix discovery of SATA devices in SAS
> > enclosures') ses_match_to_enclosure() is calling sas_get_address(),
> > which is coming from commit bcf508c13385 ('scsi_transport_sas: add
> > function to get SAS endpoint address'). sas_get_address() itself
> > calls sas_sdev_to_rdev() which BUG_ON()s if a given scsi_device's
> > rphy is not a SAS_END_DEVICE.
>
> Is the BUG_ON the problem? you're supposed to gate this call with
> is_sas_attached().
>
> > As SAS Enclosure is a SAS expander device,
>
> This isn't necessarily true. There are several separated enclosure
> chips even in the SAS world (although most of the new ones are
> integrated).
Maybe change it to "As a SAS enclosure can be a SAS expander device, [..]"
>
> > we really shouldn't tie the lookup of a SAS address to the SAS End
> > Device but the sas_rphy, which holds the address information.
>
> This is conceptually wrong. A wide end device may have many rphys
> forming a port. In that case the end device address is likely to be
> only one of the rphy addresses ... how do you know this code picks the
> right one?
>
> > Fixes: 3f8d6f2a0 ('ses: fix discovery of SATA devices in SAS
> > enclosures')
> > Cc: stable@xxxxxxxxxxxxxxx # v4.5+
>
> What's the actual bug being fixed here?
This is the callchain I have:
ses_init()
`-> scsi_register_interface()
`-> class_interface_register()
`-> ses_intf_add()
`-> ses_match_to_enclosure()
`-> sas_get_address()
`-> sas_sdev_to_rdev()
`-> BUG_ON(rphy->identify.device_type != SAS_END_DEVICE);
`-> KABOOM, Bug report, yelling release manager, etc..
Unfortunately I do not have a SAS enclosure here so all I could do was
read the spec and code and have the customer test the patch.
But from my git archeology:
Since 3f8d6f2a0 sas_match_to_enclosure() is calling
sas_get_address(). Which in turn is calling sas_sdev_to_rdev() and so
on...
The thing is, in sas_get_address() we want to get the address of a sas
device, don't we?
And looking at the UML diagram in the SAS spec, we see an enclosure as
well as an end device do have a rphy attached to it, which in turn has
a SAS address.
So where is the point in fixing the SAS address retreival to end
devices and not the rphy?
Johannes
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