linux-kernel - Re: i8k: Don't revert affinity in i8k

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Date:	Tue, 19 Aug 2014 22:34:01 +1000
From:	Con Kolivas <kernel@...ivas.org>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Sam Asadi <asadi.samuel@...il.com>, gregkh@...uxfoundation.org,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
	Andreas Mohr <andi@...as.de>
Subject: Re: i8k: Don't revert affinity in i8k_smm

On Mon, 18 Aug 2014 07:32:15 PM Guenter Roeck wrote:
> On Tue, Aug 19, 2014 at 09:19:55AM +1000, Con Kolivas wrote:
> > As a followup to this discussion:
> > 
> > On Tue, 15 Jul 2014 08:01:13 PM Sam Asadi wrote:
> > > Commit f36fdb9f0266 (i8k: Force SMM to run on CPU 0) adds support
> > > for multi-core CPUs to the driver. Unfortunately, that causes it
> > > to fail loading if compiled without SMP support, at least on
> > > 32 bit kernels. Kernel log shows "i8k: unable to get SMM Dell
> > > signature", and function i8k_smm is found to return -EINVAL.
> > > 
> > > Testing revealed that the culprit is the missing return value check
> > > of set_cpus_allowed_ptr.
> > 
> > It appears that the original commit f36fdb9f0266 changes the affinity for
> > the duration of i8k_smm function and then unconditionally reverts the
> > affinity to the old cpu mask regardless of whether the function succeeds
> > or fails. As this must run on CPU 0 at all times it does not make sense
> > to revert the affinity at the end of the function. Proposed patch
> > attached.
> 
> Sorry, I must have missed the rest of the discussion. What problem is this
> patch supposed to fix ? Or, in other words, is there a problem with the
> current code ? I also don't really understand the argument above. Why does
> it not make sense to revert to the original affinity ? After all, only the
> SMM call must run on CPU 0. Why does it not make sense to let the rest of
> the code run on another CPU ?

My mistake. If only the i8k_smm function needs to run on CPU 0 then it is 
appropriate to return affinity to the previous CPU mask. Please disregard and 
apologies for the noise.

Thanks,
Con
-- 
-ck

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