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

From: Jason Gunthorpe <jgg@ziepe.ca>
To: Leon Romanovsky <leon@kernel.org>
Cc: Gal Pressman <galpress@amazon.com>,
	Doug Ledford <dledford@redhat.com>,
	linux-rdma@vger.kernel.org,
	Alexander Matushevsky <matua@amazon.com>,
	Yossi Leybovich <sleybo@amazon.com>
Subject: Re: [PATCH for-next] RDMA/nldev: Add copy-on-fork attribute to get sys command
Date: Tue, 6 Apr 2021 11:50:25 -0300	[thread overview]
Message-ID: <20210406145025.GA227011@ziepe.ca> (raw)
In-Reply-To: <YGwDQNg3poUONNkv@unreal>

On Tue, Apr 06, 2021 at 09:44:16AM +0300, Leon Romanovsky wrote:
> On Mon, Apr 05, 2021 at 07:15:32PM -0300, Jason Gunthorpe wrote:
> > 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
> 
> The more data the better chance that it will be missed.
> It is much saner to add last commit.

I don't know, there is alot of automation here we need to ensure that
none of it triggers unless all the required commits are present. I
would list all the tops of all the 'fixes' chains.

> > And email Sasha to see if there is a magic text we can add to prevent
> > auto backporting
> 
> Don't add Fixes, maybe?

Then it randomly AI matches on the commit text and we loose even the
protection of the fixes lines

Jason