Re: find_get_entries_tag regression bisected

[Matthew Wilcox]

On Sat, Feb 16, 2019 at 09:29:48AM -0800, Matthew Wilcox wrote:
> On Sat, Feb 16, 2019 at 07:35:11AM -0800, Matthew Wilcox wrote:
> > Another way to fix this would be to mask the address in dax_entry_mkclean(),
> > but I think this is cleaner.
> 
> That's clearly rubbish, dax_entry_mkclean() can't possibly mask the
> address.  It might be mis-aligned in another process.  But ... if it's
> misaligned in another process, dax_entry_mkclean() will only clean the first
> PTE associated with the PMD; it won't clean the whole thing.  I think we need
> something like this:

Nope, this isn't enough.  It's _necessary_ to find the processes that
have part of this PMD page mapped, but not the start of it.  But it's
not _sufficient_ because it'll still only mkclean the first PTE.  So we
need a loop.  I'm feeling a bit over my head here.  I may have a go at
a fuller fix, but if someone else wants to have a go at it, be my guest!

(feeling massively unqualified for the task at hand ;-)