Re: [PATCHv2] vsock: Fix blocking ops call in prepare_to_wait

[Laura Abbott]

On 03/14/2016 12:24 PM, David Miller wrote:
> From: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxxxxxxx>
> Date: Fri, 11 Mar 2016 13:39:23 +0100
>
> > I think I found a problem with the patch submitted by Laura Abbott
> > ( https://lkml.org/lkml/2016/2/4/711 ): we might miss wakeups.
> > Since the condition is not checked between the prepare_to_wait and the
> > schedule(), if a wakeup happens after the condition is checked but before
> > the sleep happens, and we miss it. ( A description of the problem can be
> > found here: http://www.makelinux.net/ldd3/chp-6-sect-2 ).
> >
> > My solution (see patch below) is to shrink the area influenced by
> > prepare_to_wait, but keeping the fragile section around the condition, and
> > keep the rest of the code in "normal" running state.  This way the sleep is
> > correct and the other functions don't need to worry.  The only caveat here
> > is that the function(s) called to verify the conditions are really not
> > allowed to sleep, so if you need synchronization in the backend of e.g.
> > vsock_stream_has_space(), you should use spinlocks and not mutexes.
> >
> > In case we want to be able to sleep while waiting for conditions, we can
> > consider this instead: https://lwn.net/Articles/628628/ .
> >
> >
> > I stumbled on this problem while working on fixing the upcoming virtio
> > backend for vsock, below is the patch I had prepared, with the original
> > message.
>
> Can someone please look at this?  Who maintains this code anyways?

Nobody was listed in MAINTAINERS. I tried cc-ing some of the e-mail addresses
of the original authors (vmware?) when sending the original patch and they
all bounced.

Thanks,
Laura