RE: [PATCH v2 4/5] cramfs: add mmap support

[Chris Brandt]

On Tuesday, August 29, 2017, Nicolas Pitre wrote:
> On Tue, 29 Aug 2017, Chris Brandt wrote:
> 
> > On Monday, August 28, 2017, Nicolas Pitre wrote:
> > > OK I moved the lock promotion right at the beginning _before_
> validating
> > > the split point. Also got a reference on the file to make sure that
> > > hasn't changed too.
> > >
> > > > While we are at it, what happens if you mmap 120Kb, then munmap()
> the
> > > middle
> > > > 40Kb.  Leaving two 40Kb VMAs with 40Kb gap between them, that is.
> Will
> > > your
> > > > ->vm_private_data be correct for both?
> > >
> > > It wouldn't, but I now changed it to contain absolute values so now it
> > > will. And if the split point lands in the hole then the code just
> > > readjusts the pgoff at the beginning of the remaining part.
> > >
> > > Here's the revised patch:
> >
> >
> > For whatever it's worth, as soon as I moved to 4.13-rc7,
> > CONFIG_CRAMFS_PHYSMEM=y crashes my XIP_KERNEL system before it can even
> > get to any console output.
> >
> > (both the old patch and the new patch)
> >
> > If CONFIG_CRAMFS_PHYSMEM is not set, my XIP system boots fine.
> >
> > However, if I boot -rc7 as a uImage, the new patch works just as good as
> > the old patch.
> 
> When not a uImage, do you mean by that a XIP kernel?

Yes, CONFIG_XIP_KERNEL.

> If so you should
> know by now from that other thread on LAK that the XIP linker script is
> broken and probably just worked by luck till now. Still, if you could
> bisect between -rc4 and -rc7 and pinpoint the change that makes it not
> work that would be better than speculations.

Note that everything else seem OK when CONFIG_XIP_KERNEL=y. It's just 
when CONFIG_XIP_KERNEL=y CONFIG_CRAMFS_PHYSMEM=y which is odd. So hopefully
that means it will be easy to track down.


Chris