Re: find_get_entries_tag regression bisected
From: Matthew Wilcox
Date: Tue Feb 26 2019 - 07:08:30 EST
On Mon, Feb 25, 2019 at 09:03:00PM -0800, Dan Williams wrote:
> On Sat, Feb 16, 2019 at 1:11 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
> > 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!
> Nothing comes to mind outside of pseudo-reverting this conversion by
> introducing a way to get back to the old semantics. If you don't see a
> path forward, us mere Xarray-mortals stand no chance.
This is a pre-existing bug. Fixing the regression is easy.