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

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Message-ID: <CA+8MBbKn3PMG5o1R377vQPV-_PPFU_ZsEp7ZpYC6=1dJZodyEQ@mail.gmail.com>
Date:	Wed, 3 Aug 2011 16:10:29 -0700
From:	Tony Luck <tony.luck@...il.com>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	linux-kernel@...r.kernel.org,
	Matt Fleming <matt.fleming@...ux.intel.com>,
	Jan Beulich <JBeulich@...ell.com>,
	Matthew Garrett <mjg@...hat.com>,
	"H. Peter Anvin" <hpa@...ux.intel.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 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.

ia64 bits look ok (they build & boot too - which is always a plus :-)

Acked-by: Tony Luck <tony.luck@...el.com>
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