Re: Question on memory commit during MR finalize()

[Paolo Bonzini]

On 20/04/20 23:00, Peter Xu wrote:
> 
> I'm still uncertain how the dirty ring branch can easily trigger this, however
> the backtrace looks really odd to me in that we're going to do memory commit
> and even sending KVM ioctls during finalize(), especially in the RCU thread...
> I never expected that.

Short answer: it is really hard to not trigger finalize() from an RCU
callback, and it's the reason why the RCU thread takes the big QEMU lock.

However, instead of memory_region_transaction_commit,
memory_region_finalize probably should do something like

    --memory_region_transaction_depth;
    assert (memory_region_transaction_depth ||
            (!memory_region_update_pending &&
             !ioeventfd_update_pending));

Paolo