Re: [PATCH] Don't race while creating a VCPU

[Avi Kivity <avi@qumranet.com>]

Anthony Liguori wrote:
> We hold qemu_mutex while machine->init() executes, which issues a VCPU create.
> We need to make sure to not return from the VCPU creation until the VCPU
> file descriptor is valid to ensure that APIC creation succeeds.
>
> However, we also need to make sure that the VCPU thread doesn't start running
> until the machine->init() is complete.  This is addressed today because the
> VCPU thread tries to grab the qemu_mutex before doing anything interesting.
> If we release qemu_mutex to wait for VCPU creation, then we open a window for
> a race to occur.
>
> This patch introduces two wait conditions.  The first lets the VCPU create
> code that runs in the IO thread to wait for a VCPU to initialize.  The second
> condition lets the VCPU thread wait for the machine to fully initialize before
> running.
>
>   

Applied, thanks.


> An added benefit of this patch is it makes the dependencies now explicit.
>
>   

Indeed.

-- 
Any sufficiently difficult bug is indistinguishable from a feature.


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