linux-kernel - Re: [Question] Missing data after DMA read transfer

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Date:	Tue, 10 May 2016 15:34:01 +0200
From:	Jerome Glisse <j.glisse@...il.com>
To:	Nicolas Morey Chaisemartin <devel@...ey-chaisemartin.com>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [Question] Missing data after DMA read transfer - mm issue with
 transparent huge page?

On Tue, May 10, 2016 at 01:15:02PM +0200, Nicolas Morey Chaisemartin wrote:
> Le 05/10/2016 à 12:01 PM, Jerome Glisse a écrit :
> > On Tue, May 10, 2016 at 09:04:36AM +0200, Nicolas Morey Chaisemartin wrote:
> >> Le 05/03/2016 à 12:11 PM, Jerome Glisse a écrit :
> >>> On Mon, May 02, 2016 at 09:04:02PM -0700, Hugh Dickins wrote:
> >>>> On Fri, 29 Apr 2016, Nicolas Morey Chaisemartin wrote:

[...]

> >> Hi,
> >>
> >> I backported the patch to 3.10 (had to copy paste pmd_protnone defitinition from 4.5) and it's working !
> >> I'll open a ticket in Redhat tracker to try and get this fixed in RHEL7.
> >>
> >> I have a dumb question though: how can we end up in numa/misplaced memory code on a single socket system?
> >>
> > This patch is not a fix, do you see bug message in kernel log ? Because if
> > you do that it means we have a bigger issue.
> I don't see any on my 3.10. I have DMA_API_DEBUG enabled but I don't think it has an impact.

My patch can't be backported to 3.10 as is, you most likely need to replace
pmd_protnone() by pmd_numa()

> > You did not answer one of my previous question, do you set get_user_pages
> > with write = 1 as a paremeter ?
> For the read from the device, yes:
>         down_read(&current->mm->mmap_sem);
>         res = get_user_pages(
>                 current,
>                 current->mm,
>                 (unsigned long) iov->host_addr,
>                 page_count,
>                 (write_mode == 0) ? 1 : 0,      /* write */
>                 0,      /* force */
>                 &trans->pages[sg_o],
>                 NULL);
>         up_read(&current->mm->mmap_sem);

As i don't have context to infer how write_mode is set above, do you mind
retesting your driver and always asking for write no matter what ?

> > Also it would be a lot easier if you were testing with lastest 4.6 or 4.5
> > not RHEL kernel as they are far appart and what might looks like same issue
> > on both might be totaly different bugs.
> Is a RPM from elrepo ok?
> http://elrepo.org/linux/kernel/el7/SRPMS/

Yes should be ok for testing.

Cheers,
Jérôme