Re: [Xen-devel] memguard_guard_stack()

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 1 May 2006, at 12:36, Jan Beulich wrote:

> Hmm, but I found this precisely because we saw a double fault due to a 
> stack overflow. Admittedly this was in the
> context of one of these IPI storms during shotdown that were fixed 
> previously, but even that shouldn't result in a stack
> overflow, should it ? Jan
How many CPUs were in the system? That code path was rather dodgy: the 
function forcibly enabled interrupts and so a single CPU could nest in 
that function up to (NR_CPUS-1) times which, if you had say 32 CPUs in 
the system could certainly cause problems. I don't think it's 
indicative of a wider problem in Xen -- for most interrupts (ones bound 
to a guest) we don't even reenable interrupt delivery while handling 
them, so nested ISRs in Xen are impossible.
I would like to understand exactly what happened in the context of your 
IPI storm (it *is* the machine restart bug we're talking about, right?) 
-- if you had much fewer than 32 CPUs then I need to check exactly how 
much stack an invocation of machine_restart() uses.
 -- Keir


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