Re: [PATCHv2 1/3] eventfd: allow atomic read and waitqueue remove

[Avi Kivity]

On 01/21/2010 06:58 PM, Davide Libenzi wrote:
> On Thu, 21 Jan 2010, Michael S. Tsirkin wrote:
>
>    
> > This is a backport of commit: 03db343a6320f780937078433fa7d8da955e6fce
> > modified in a way that introduces some code duplication on the one hand,
> > but reduces the risk of regressing existing eventfd users on the other
> > hand.
> >
> > KVM needs a wait to atomically remove themselves from the eventfd
> > ->poll() wait queue head, in order to handle correctly their IRQfd
> > deassign operation.
> >
> > This patch introduces such API, plus a way to read an eventfd from its
> > context.
> >
> > Signed-off-by: Michael S. Tsirkin<mst@xxxxxxxxxx>
> > ---
> >
> > Avi, Davidel, how about only including the following part for -stable
> > then?  Reason is, I still would like to be able to use irqfd there, and
> > getting spurious interrupts 100% of times unmask is done isn't a very
> > good idea IMO ...
> >      
> It's the same thing. Unless there are *real* problems in KVM due to the
> spurious ints, I still think this is .33 material.
>    

I agree.

But I think we can solve this in another way in .32: we can clear the 
eventfd from irqfd->inject work, which is in process context.  The new 
stuff is only needed for lockless clearing, no?

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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