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Re: [Xen-devel] [RFC][PATCH] walking the page lists needs the page_alloc

To: "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [RFC][PATCH] walking the page lists needs the page_alloc lock
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Fri, 13 Aug 2010 08:06:31 +0100
Cc: Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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>>> On 13.08.10 at 08:46, Keir Fraser <keir.fraser@xxxxxxxxxxxxx> wrote:
> On 13/08/2010 07:40, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>>> Sorry, my intention was to say that changes to the debug-key printouts
>>> are safe, not that they didn't require changes.
>>> The debug-key printouts (in particular the NUMA one) are where I
>>> actually hit this bug on a running system.
>> But then, to avoid a hanging system, these should be trylock-s
>> rather than plain locks, shouldn't they?
> Why? The handler is called in softirq context. It should be safe to spin.

Hmm, indeed. I was looking at others, and at least
domain_dump_evtchn_info() also uses a trylock - apparently for
no good reason.


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