From: Keir Fraser <keir.fraser@eu.citrix.com>
Subject: Re: [Patch] continue_hypercall_on_cpu rework using
	tasklets
Date: Thu, 15 Apr 2010 09:22:04 +0100
Message-ID: <C7EC8B3C.11577%keir.fraser@eu.citrix.com>
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On 15/04/2010 09:13, "Keir Fraser" <keir.fraser@eu.citrix.com> wrote:

> Better hope so or e.g.,
> acpi_enter_sleep
> ->continue_hypercall_on_cpu(enter_state_helper)
> ->enter_state
> ->freeze_domains
> ->domain_pause
> ->vcpu_sleep_sync
> ->sync_vcpu_execstate
> Also wouldn't work.

Actually that's a good example because it now won't work, but for other
reasons! The hypercall continuation can interrupt another vcpu's execution,
and then try to synchronously pause that vcpu. Which will deadlock.

Luckily I think we can re-jig this code to freeze_domains() before doing the
continue_hypercall_on_cpu(). I've cc'ed one of the CPU RAS guys. :-)

 -- Keir