Re: [Qemu-devel] [RFC PATCH] fix select(2) race between main_loop_wait and qemu_aio_wait

[Avi Kivity]

On 03/05/2012 11:07 AM, Jan Kiszka wrote:
> On 2012-03-05 09:34, Paolo Bonzini wrote:
> > This is quite ugly.  Two threads, one running main_loop_wait and
> > one running qemu_aio_wait, can race with each other on running the
> > same iohandler.  The result is that an iohandler could run while the
> > underlying socket is not readable or writable, with possibly ill effects.
>
> Hmm, isn't it a problem already that a socket is polled by two threads
> at the same time? Can't that be avoided?

Could it be done simply by adding a mutex there?  It's hardly a clean
fix, but it's not a clean problem.

> Long-term, I'd like to cut out certain file descriptors from the main
> loop and process them completely in separate threads (for separate
> locking, prioritization etc.). Dunno how NBD works, but maybe it should
> be reworked like this already.

Ideally qemu_set_fd_handler2() should be made thread local, and each
device thread would run a copy of the main loop, just working on
different data.

-- 
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