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

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Message-ID: <1312454219.10579.80.camel@mfleming-mobl1.ger.corp.intel.com>
Date:	Thu, 04 Aug 2011 11:36:59 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	john stultz <johnstul@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, Jan Beulich <JBeulich@...ell.com>,
	Matthew Garrett <mjg@...hat.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Tony Luck <tony.luck@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Alessandro Zummo <a.zummo@...ertech.it>
Subject: Re: [PATCH] x86, efi: Don't recursively acquire rtc_lock

On Thu, 2011-08-04 at 03:22 -0700, john stultz wrote:
> On Wed, Aug 3, 2011 at 2:04 PM, Matt Fleming <matt@...sole-pimps.org> wrote:
> > From: Matt Fleming <matt.fleming@...ux.intel.com>
> >
> > A deadlock was introduced on x86 in commit ef68c8f87ed1 ("x86:
> > Serialize EFI time accesses on rtc_lock") because efi_get_time() and
> > friends can be called with rtc_lock already held by
> > read_persistent_time(), e.g.
> >
> > timekeeping_init()
> >    read_persistent_clock()     <-- acquire rtc_lock
> >        efi_get_time()
> >            phys_efi_get_time() <-- acquire rtc_lock <DEADLOCK>
> >
> > Move the locking up into the caller of efi.get_time() and provide some
> > wrappers for use in other parts of the kernel instead of calling
> > efi.get_time(), etc directly. This way we can hide the rtc_lock dance
> > inside of arch/x86.
> 
> Sorry if this should be obvious, but is there a reason your not using
> your own internal lock for serializing the efi bits rather then using
> the rtc_lock?

Jan wrote the original code that started using the rtc_lock inside the
EFI bits here, ef68c8f87ed1 ("x86: Serialize EFI time accesses on
rtc_lock").

Jan?
 
-- 
Matt Fleming, Intel Open Source Technology Center

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