Re: [Qemu-devel] [PATCH] vcpu: create vcpu thread with QEMU_THREAD_DETACHED mode

[Paolo Bonzini]

On 28/01/2018 05:14, CheneyLin wrote:
>> This is dangerous, it risks introducing use-after-free bugs in the vCPU
>> thread.  Can you instead add a qemu_thread_join call where the vCPU goes
>> away (e.g. unrealize, I'm not sure)?
> 
> 1. If another thread calls qemu_thread_join, it will block until vcpu thread 
> exit.

Sure, but that's not a problem.  If the code is written correctly, it
will only block for a very short time.  In particular, in this case
we'll block anyway in cpu_remove_sync.  The fix is just to change that
function from qemu_cond_wait to qemu_thread_join.

> 2. As vcpu exits, its resources should be freed ,which will not be used any 
> more(e.g. user space stack), how can we get use-after-free bugs?

Use-after-free bugs happen in the vCPU thread if the vCPU resources are
freed just before the vCPU thread exits.

Paolo