linux-kernel - Re: [PATCH] hwmon: (fam15h_power) Disable preemption when reading registers

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Date:	Wed, 1 Jun 2016 15:41:26 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Guenter Roeck <linux@...ck-us.net>, Ingo Molnar <mingo@...nel.org>
Cc:	linux-hwmon@...r.kernel.org, X86 ML <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Rui Huang <ray.huang@....com>,
	Sherry Hurwitz <sherry.hurwitz@....com>
Subject: Re: [PATCH] hwmon: (fam15h_power) Disable preemption when reading
 registers

On Wed, Jun 01, 2016 at 06:22:59AM -0700, Guenter Roeck wrote:
> An explanation would be helpful. Is this a bug fix ?

That's a good point - yes, it is necessary. Both smp_processor_id()
*and* smp_call_function_many() need to be called with preemption
disabled.

It did fire the BUG thing in check_preemption_disabled() with 4.7-rc1
here without those fixes.

But, we need the other patch too -

"[PATCH] x86/cpu/AMD: Extend X86_FEATURE_TOPOEXT workaround to newer models"

because the cpumask generation in read_registers() doesn't work on those
Carrizo CPUs.

IINM, the breakage came in during this merge window so we don't have to
CC:stable but both should be sent to Linus as fixes for 4.7.

You could sync with Ingo who takes/acks what... but they could go
through tip and hwmon tree too, I don't see a hard dependency between
the two - they'd only need to be in 4.7-final.

Thanks.

-- 
Regards/Gruss,
    Boris.

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