Re: WARNING in __mmdrop

[Jason Wang]

On 2019/7/23 äå6:42, Michael S. Tsirkin wrote:
> On Tue, Jul 23, 2019 at 04:42:19PM +0800, Jason Wang wrote:
> > > So how about this: do exactly what you propose but as a 2 patch series:
> > > start with the slow safe patch, and add then return uaddr optimizations
> > > on top. We can then more easily reason about whether they are safe.
> >
> > If you stick, I can do this.
> So I definitely don't insist but I'd like us to get back to where
> we know existing code is very safe (if not super fast) and
> optimizing from there.  Bugs happen but I'd like to see a bisect
> giving us "oh it's because of XYZ optimization" and not the
> general "it's somewhere within this driver" that we are getting
> now.


Syzbot has bisected to the commit of metadata acceleration in fact :)


> Maybe the way to do this is to revert for this release cycle
> and target the next one. What do you think?


I would try to fix the issues consider packed virtqueue which may use 
this for a good performance number. But if you insist, I'm ok to revert. 
Or maybe introduce a config option to disable it by default (almost all 
optimized could be ruled out).

Thanks