linux-kernel - Re: [PATCH] Xen: Fix pte unpin BUG when !CONFIG

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Date:	Tue, 09 Sep 2008 23:26:22 +0100
From:	Alex Nixon <alex.nixon@...rix.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] Xen: Fix pte unpin BUG when !CONFIG_SMP

Jeremy Fitzhardinge wrote:
> Alex Nixon wrote:
>   
>>
>> Here's the backtrace of the BUG() the patch addresses.  Now you've
>> pointed it out - I see the asymmetry - and also suspect some ptes are
>> being left pinned.
>>
>> I'm having trouble finding a cleaner solution which solves this but
>> doesn't incite more BUGs.
>> Perhaps you have an idea?
>>     
>
> Right, I see.  We shouldn't be pinning ptes on attachment in
> xen_alloc_ptpage() if we're not using split pte locks.
>
>     J
>
>   
Hmm ok.  I'll search further for a solution which fixes things more 
officially (and deals with the CONFIG_SMP && (NR_CPUS < 
CONFIG_SPLIT_PTLOCK_CPUS) case, which I just realized is also broken, 
and isn't fixed by this patch).

In the meantime, at least UP is now usable.

- Alex
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