Re: [libvirt] [PATCH] virCommand: Don't misuse the eventloop for async IO
On 12.02.2013 21:35, Eric Blake wrote:
On 02/08/2013 07:28 AM, Michal Privoznik wrote:
> Currently, if a command wants to do asynchronous IO, a callback
> is registered in the libvirtd eventloop to handle writes and
> reads. However, there's a race in virCommandWait. The eventloop
> may already be executing the callback, while virCommandWait is
> mangling internal state of virCommand. To deal with it, we need
> to either introduce locking or spawn a separate thread where we
> poll() on stdio from child. The former, however, requires to
> unlock all mutexes held, as the event loop may execute other
> callbacks which tries to lock one of the mutexes, deadlock and
> thus never wake us up. So it's safer to spawn a separate thread.
> ---
>
> This is an alternative to:
>
> https://www.redhat.com/archives/libvir-list/2013-February/msg00352.html
I definitely like this version better - callers are not impacted. You
may still want to wait for danpb's review, but you have my:
ACK.
I've done some stress testing (repetitive suspend + resume of several
domains at once - with compression of image enabled, iohelper, ...) and
since it didn't stuck anywhere or broke in any other way I took your ACK
sufficient and pushed. This is a bugfix of a race not enhancement after all.
Michal