linux-kernel - Re: applesmc oops in 3.10/3.11

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Date:	Wed, 2 Oct 2013 13:59:31 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Chris Murphy <bugzilla@...orremedies.com>
Cc:	Henrik Rydberg <rydberg@...omail.se>,
	Josh Boyer <jwboyer@...oraproject.org>, khali@...ux-fr.org,
	lm-sensors@...sensors.org,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: Re: applesmc oops in 3.10/3.11

On Wed, Oct 02, 2013 at 12:33:00PM -0600, Chris Murphy wrote:
> 
> On Oct 2, 2013, at 12:02 PM, Guenter Roeck <linux@...ck-us.net> wrote:
> 
> > On Wed, Oct 02, 2013 at 07:24:10PM +0200, Henrik Rydberg wrote:
> >> On Wed, Oct 02, 2013 at 09:47:18AM -0700, Guenter Roeck wrote:
> >>> On Wed, Oct 02, 2013 at 06:34:18PM +0200, Henrik Rydberg wrote:
> >>>>>>> One thing I have seen in all logs is the earlier "send_byte fail" message, so
> >>>>>>> I think that is a pre-requisite.
> >>>>>> 
> >>>>>> Not necessarily - it could be that the patch actually fixes the root
> >>>>>> cause. One possible scenario is that on recent SMCs, some of the
> >>>>>> commands produce more data than we actually read. This would
> >>>>>> eventually lead to both data corruption and overflow somwhere in the
> >>>>>> SMC internals.  If the original SMC error is interpreted as a read
> >>>>>> buffer overflow, then that problem should be fixed with this patch.
> >>>>>> 
> >>>>> 
> >>>>> Good point.
> >>>>> 
> >>>>> But shouldn't we at least get the "flushed %d bytes" warning message in this case ?
> >>>> 
> >>>> The explanation I have there is that the (newer) SMC needs the
> >>>> application to read the 'no more bytes' or it will get confused. It
> >>>> makes sense, if the number of bytes to read is no longer specified.
> >>>> 
> >>> You mean that just reading from APPLESMC_CMD_PORT would solve the problem ?
> >>> That might make sense.
> >> 
> >> It also points at the possibility of a smaller patch to test, but I
> >> have not had the time to check this very deeply myself:
> >> 
> > I like this patch much more than the previous patch. Chris, can you test it ?
> 
> Yes. Building now. What kernel message should I be looking for? At least on 2011 and 2012 laptops I have yet to see an Oops related to smc. The kernel with previous patch at least is not causing problems on them so far, which works well as I can test more on the 2008 model.
> 
None, if I understand correctly and if the patch really fixes the root cause
of the problem.

Guenter
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