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

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Message-Id: <4E3C30C602000078000740D5@nat28.tlf.novell.com>
Date:	Fri, 05 Aug 2011 18:04:54 +0100
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	<matt@...sole-pimps.org>
Cc:	<fenghua.yu@...el.com>, <tony.luck@...el.com>,
	<hpa@...ux.intel.com>, <mjg@...hat.com>, <a.zummo@...ertech.it>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86, efi: Don't recursively acquire rtc_lock

>>> Matt Fleming  08/04/11 11:33 AM >>>
>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()

Virtual platforms will have to take care of the serialization in the
host anyway, so the guest side implementation of getwallclock et al
is entirely unaffected.

>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.

I agree to the "as few places as possible" part.

Jan

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