linux-kernel - Re: [PATCH] SAS: use sas_rphy instead of sas_end

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Message-Id: <1470928175.2334.9.camel@linux.vnet.ibm.com>
Date:	Thu, 11 Aug 2016 08:09:35 -0700
From:	James Bottomley <jejb@...ux.vnet.ibm.com>
To:	Johannes Thumshirn <jthumshirn@...e.de>,
	"Martin K . Petersen" <martin.petersen@...cle.com>
Cc:	Hannes Reinecke <hare@...e.de>,
	Linux SCSI Mailinglist <linux-scsi@...r.kernel.org>,
	Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>,
	stable@...r.kernel.org, #@...e.de, v4.5+@...e.de
Subject: Re: [PATCH] SAS: use sas_rphy instead of sas_end_device to obtain
 address.

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).

>  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@...r.kernel.org # v4.5+

What's the actual bug being fixed here?

James