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

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 12.08.10 at 18:37, Tim Deegan <Tim.Deegan@xxxxxxxxxx> wrote:
> At 16:09 +0100 on 12 Aug (1281629364), Jan Beulich wrote:
>> >>> On 23.07.10 at 15:49, Tim Deegan <Tim.Deegan@xxxxxxxxxx> wrote:
>> > There are a few places in Xen where we walk a domain's page lists
>> > without holding the page_alloc lock.  They race with updates to the page
>> > lists, which are normally rare but can be quite common under PoD when
>> > the domain is close to its memory limit and the PoD reclaimer is busy.
>> > This patch protects those places by taking the page_alloc lock.
>> > 
>> > I think this is OK for the two debug-key printouts - they don't run from
>> > irq context and look deadlock-free.  The tboot change seems safe too
>> 
>> While the comment says the patch would leave debug key printouts
>> alone, ...
> 
> 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?

Jan


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