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Subject: Re: [PATCH] x86, efi: Don't recursively acquire rtc_lock
From: john stultz <johnstul@us.ibm.com>
To: Matt Fleming <matt@console-pimps.org>
Cc: linux-kernel@vger.kernel.org, Matt Fleming <matt.fleming@linux.intel.com>,
        Jan Beulich <JBeulich@novell.com>, Matthew Garrett <mjg@redhat.com>,
        "H. Peter Anvin" <hpa@linux.intel.com>,
        Tony Luck <tony.luck@intel.com>, Fenghua Yu <fenghua.yu@intel.com>,
        Alessandro Zummo <a.zummo@towertech.it>
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On Wed, Aug 3, 2011 at 2:04 PM, Matt Fleming <matt@console-pimps.org> wrote:
> From: Matt Fleming <matt.fleming@linux.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?

thanks
-john