Re: [PATCH for-next] RDMA/nldev: Add copy-on-fork attribute to get sys command

[Jason Gunthorpe <jgg@ziepe.ca>]

On Mon, Apr 05, 2021 at 04:09:39PM +0300, Gal Pressman wrote:
> On 05/04/2021 15:39, Leon Romanovsky wrote:
> > On Mon, Apr 05, 2021 at 03:15:18PM +0300, Gal Pressman wrote:
> >> On 05/04/2021 14:57, Leon Romanovsky wrote:
> >>> On Mon, Apr 05, 2021 at 02:47:21PM +0300, Gal Pressman wrote:
> >>>> The new attribute indicates that the kernel copies DMA pages on fork,
> >>>> hence libibverbs' fork support through madvise and MADV_DONTFORK is not
> >>>> needed.
> >>>>
> >>>> The introduced attribute is always reported as supported since the
> >>>> kernel has the patch that added the copy-on-fork behavior. This allows
> >>>> the userspace library to identify older vs newer kernel versions.
> >>>> Extra care should be taken when backporting this patch as it relies on
> >>>> the fact that the copy-on-fork patch is merged, hence no check for
> >>>> support is added.
> >>>
> >>> Please be more specific, add SHA-1 of that patch and wrote the same
> >>> comment near "err = nla_put_u8(msg, RDMA_NLDEV_SYS_ATTR_COPY_ON_FORK,
> >>> 1);" line.
> >>>
> >>> Thanks
> >>
> >> Should I put the original commit here? There were quite a lot of bug fixes and
> >> followups that are required.
> > 
> > IMHO, the last commit SHA will be enough, the one that has working
> > functionality from your POV.
> 
> OK, so that would be:
> 4eae4efa2c29 ("hugetlb: do early cow when page pinned on src mm")

No, lets put them all

And I'd mark them with a Fixes: and a huge comment saying not to
backport this and that the Fixes lines exist to *prevent* tooling from
wrongly backporting to kernels that cannot support this.

And email Sasha to see if there is a magic text we can add to prevent
auto backporting

> Which I now realize for-next isn't rebased on top of it yet, so these patches
> should be applied after rebasing to v5.12-rc5.

I will sort it out

Jason