linux-kernel - Re: [PATCH] x86, efi: Don't recursively acquire rtc

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Message-ID: <1312450416.10579.70.camel@mfleming-mobl1.ger.corp.intel.com>
Date:	Thu, 04 Aug 2011 10:33:36 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Jan Beulich <jbeulich@...ell.com>
Cc:	linux-kernel@...r.kernel.org, fenghua.yu@...el.com,
	tony.luck@...el.com, hpa@...ux.intel.com, mjg@...hat.com,
	a.zummo@...ertech.it
Subject: Re: [PATCH] x86, efi: Don't recursively acquire rtc_lock

On Thu, 2011-08-04 at 03:53 +0100, Jan Beulich wrote:
> 
> Seems the wrong approach to me: The call happening with the lock held
> is the wrong part imo, and hence the fix ought to be to drop the lock
> there.

But what about other platforms that provide a get_wallclock()
implementation such as the kvm or xen code? If we called get_wallclock()
without rtc_lock held we'd be requiring everyone to lock it in their
clock code, which is unnecessary work and increases the amount of code
that touches rtc_lock (not to mention spreading it across several
files).

I think it's much better to do the locking as high up the callstack as
possible and preferably in as few places as possible.

-- 
Matt Fleming, Intel Open Source Technology Center

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