Re: [PATCH] mm/hmm: Simplify hmm_vma_walk_pud slightly

[Jason Gunthorpe <jgg@ziepe.ca>]

On Thu, Mar 12, 2020 at 02:40:08PM +0000, Steven Price wrote:
> On 12/03/2020 14:27, Jason Gunthorpe wrote:
> > On Thu, Mar 12, 2020 at 10:28:13AM +0000, Steven Price wrote:
> > > By refactoring to deal with the !pud_huge(pud) || !pud_devmap(pud)
> > > condition early it's possible to remove the 'ret' variable and remove a
> > > level of indentation from half the function making the code easier to
> > > read.
> > > 
> > > No functional change.
> > > 
> > > Signed-off-by: Steven Price <steven.price@arm.com>
> > > Thanks to Jason's changes there were only two code paths left using
> > > the out_unlock label so it seemed like a good opportunity to
> > > refactor.
> > 
> > Yes, I made something very similar, what do you think of this:
> > 
> > https://github.com/jgunthorpe/linux/commit/93f0ed42ab3f9ceb27b58fb7c7c3ecaf60f16b36
> 
> Even better! Sorry I didn't realise you'd already done this. I just saw that
> the function was needlessly complicated after your fix, so I thought I'd do
> a drive-by cleanup since part of the mess was my fault! :)

No worries, I've got a lot of patches for hmm_range_fault right now,
just trying to organize them, test them and post them. Haven't posted
that one yet.

Actually, while you are looking at this, do you think we should be
adding at least READ_ONCE in the pagewalk.c walk_* functions? The
multiple references of pmd, pud, etc without locking seems sketchy to
me.

Jason