Re: [PATCH] mm: mmu_notifier: re-fix freed page still mapped in secondary MMU

[Robin Holt <holt@sgi.com>]

On Thu, Apr 18, 2013 at 02:52:31AM +0800, Xiao Guangrong wrote:
> On 04/18/2013 02:45 AM, Robin Holt wrote:
> 
> >>>>>>> For the v3.10 release, we should work on making this more
> >>>>>>> correct and completely documented.
> >>>>>>
> >>>>>> Better document is always welcomed.
> >>>>>>
> >>>>>> Double call ->release is not bad, like i mentioned it in the changelog:
> >>>>>>
> >>>>>> it is really rare (e.g, can not happen on kvm since mmu-notify is unregistered
> >>>>>> after exit_mmap()) and the later call of multiple ->release should be
> >>>>>> fast since all the pages have already been released by the first call.
> >>>>>>
> >>>>>> But, of course, it's great if you have a _light_ way to avoid this.
> >>>>>
> >>>>> Getting my test environment set back up took longer than I would have liked.
> >>>>>
> >>>>> Your patch passed.  I got no NULL-pointer derefs.
> >>>>
> >>>> Thanks for your test again.
> >>>>
> >>>>>
> >>>>> How would you feel about adding the following to your patch?
> >>>>
> >>>> I prefer to make these changes as a separate patch, this change is the
> >>>> improvement, please do not mix it with bugfix.
> >>>
> >>> I think your "improvement" classification is a bit deceiving.  My previous
> >>> patch fixed the bug in calling release multiple times.  Your patch without
> >>> this will reintroduce that buggy behavior.  Just because the bug is already
> >>> worked around by KVM does not mean it is not a bug.
> >>
> >> As your tested, calling ->release() multiple times can work, but just make your
> >> testcase more _slower_. So your changes is trying to speed it up - it is a
> >> improvement.
> >>
> >> Well, _if_ it is really a bug, could you please do not fix two bugs in one patch?
> > 
> > The code, as is, does not call ->release() multiple times.  Your code
> > changes the behavior to call it multiple times.  You are introducing the
> > bug by your code changes.  Why not fix the bug you create in the patch
> > which creates it?
> 
> Andrew, your thought?
> 

What ever happened with this?

Robin

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