Re: [PATCH v14 00/74] Convert page cache to XArray

[Ross Zwisler]

On Thu, Jun 28, 2018 at 01:39:09AM -0700, Matthew Wilcox wrote:
> On Wed, Jun 27, 2018 at 01:44:38PM -0600, Ross Zwisler wrote:
> > On Wed, Jun 27, 2018 at 04:05:29AM -0700, Matthew Wilcox wrote:
> > > On Tue, Jun 19, 2018 at 10:16:38AM -0700, Matthew Wilcox wrote:
> > > > I think I see a bug.  No idea if it's the one you're hitting ;-)
> > > > 
> > > > I had been intending to not use the 'entry' to decide whether we were
> > > > waiting on a 2MB or 4kB page, but rather the xas.  I shelved that idea,
> > > > but not before dropping the DAX_PMD flag being passed from the PMD
> > > > pagefault caller.  So if I put that back ...
> > > 
> > > Did you get a chance to test this?
> > 
> > With this patch it doesn't deadlock, but the test dies with a SIGBUS and we
> > hit a WARN_ON in the DAX code:
> > 
> > WARNING: CPU: 5 PID: 1678 at fs/dax.c:226 get_unlocked_entry+0xf7/0x120
> > 
> > I don't have a lot of time this week to debug further.  The quickest path to
> > victory is probably for you to get this reproducing in your test setup.  Does
> > XFS + DAX + generic/340 pass for you?
> 
> I won't be back in front of my test box until Tuesday, but that test
> does work for me because I couldn't get your instructions to give me a
> 2MB aligned DAX setup.  I had to settle for 4k, so none of the 2MB stuff
> has been tested properly.

Ah.  I've documented both my qemu setup and my filesystem setup here:

https://nvdimm.wiki.kernel.org/pmem_in_qemu
https://nvdimm.wiki.kernel.org/2mib_fs_dax

This should be enough to get you up and running in QEMU and able to reliably
get filesystem DAX PMD faults.