linux-kernel - Re: [PATCH v2] x86: Don't recursively acquire rtc

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Date:	Mon, 10 Oct 2011 08:45:36 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	johnstultz <johnstul@...ibm.com>,
	Matthew Garrett <mjg@...hat.com>, linux-kernel@...r.kernel.org,
	Jan Beulich <jbeulich@...ell.com>, Avi Kivity <avi@...hat.com>,
	"Zhang, Rui" <rui.zhang@...el.com>
Subject: Re: [PATCH v2] x86: Don't recursively acquire rtc_lock


* Matt Fleming <matt@...sole-pimps.org> wrote:

> On Tue, 2011-08-30 at 17:17 +0100, Matt Fleming wrote:
> > (Adding Jan and Avi, apparently git send-email doesn't grok Acked-by's)
> > 
> > On Tue, 2011-08-30 at 17:12 +0100, Matt Fleming wrote:
> > > From: Matt Fleming <matt.fleming@...el.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>
> > > 
> > > To fix this let's push the locking down into the get_wallclock() and
> > > set_wallclock() implementations. Only the clock implementations that
> > > access the x86 RTC directly need to acquire rtc_lock, so it makes
> > > sense to push the locking down into the rtc, vrtc and efi code.
> > > 
> > > The virtualization implementations don't require rtc_lock to be held
> > > because they provide their own serialization.
> > > 
> > > Signed-off-by: Matt Fleming <matt.fleming@...el.com>
> > > Acked-by: Jan Beulich <jbeulich@...ell.com>
> > > Acked-by: Avi Kivity <avi@...hat.com> [for the virtualization aspect]
> 
> Ping? It's -rc8 and 32-bit EFI machines still don't boot.

Don't know the status of this - Thomas?

Thanks,

	Ingo
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