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

From: Leon Romanovsky <leon@kernel.org>
To: Gal Pressman <galpress@amazon.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>,
	Doug Ledford <dledford@redhat.com>,
	linux-rdma@vger.kernel.org,
	Alexander Matushevsky <matua@amazon.com>,
	Yossi Leybovich <sleybo@amazon.com>,
	Jason Gunthorpe <jgg@ziepe.ca>
Subject: Re: [PATCH for-next] RDMA/nldev: Add copy-on-fork attribute to get sys command
Date: Mon, 5 Apr 2021 15:39:57 +0300	[thread overview]
Message-ID: <YGsFHWU8Hqd5LADT@unreal> (raw)
In-Reply-To: <d8ec4f81-25a6-7243-12c4-af4f5b64a27f@amazon.com>

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.

Thanks

> 
> >>
> >> Copy-on-fork attribute is read-only, trying to change it through the set
> >> sys command will result in an error.
> >>
> >> Signed-off-by: Gal Pressman <galpress@amazon.com>
> >> ---
> >> PR was sent:
> >> https://github.com/linux-rdma/rdma-core/pull/975
> >> ---
> >>  drivers/infiniband/core/nldev.c  | 19 ++++++++++++++-----
> >>  include/uapi/rdma/rdma_netlink.h |  2 ++
> >>  2 files changed, 16 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/drivers/infiniband/core/nldev.c b/drivers/infiniband/core/nldev.c
> >> index b8dc002a2478..87c68301c25b 100644
> >> --- a/drivers/infiniband/core/nldev.c
> >> +++ b/drivers/infiniband/core/nldev.c
> >> @@ -146,6 +146,7 @@ static const struct nla_policy nldev_policy[RDMA_NLDEV_ATTR_MAX] = {
> >>       [RDMA_NLDEV_ATTR_UVERBS_DRIVER_ID]      = { .type = NLA_U32 },
> >>       [RDMA_NLDEV_NET_NS_FD]                  = { .type = NLA_U32 },
> >>       [RDMA_NLDEV_SYS_ATTR_NETNS_MODE]        = { .type = NLA_U8 },
> >> +     [RDMA_NLDEV_SYS_ATTR_COPY_ON_FORK]      = { .type = NLA_U8 },
> >>  };
> >>
> >>  static int put_driver_name_print_type(struct sk_buff *msg, const char *name,
> >> @@ -1693,12 +1694,19 @@ static int nldev_sys_get_doit(struct sk_buff *skb, struct nlmsghdr *nlh,
> >>
> >>       err = nla_put_u8(msg, RDMA_NLDEV_SYS_ATTR_NETNS_MODE,
> >>                        (u8)ib_devices_shared_netns);
> >> -     if (err) {
> >> -             nlmsg_free(msg);
> >> -             return err;
> >> -     }
> >> +     if (err)
> >> +             goto err_nlmsg_free;
> >> +
> >> +     err = nla_put_u8(msg, RDMA_NLDEV_SYS_ATTR_COPY_ON_FORK, 1);
> >> +     if (err)
> >> +             goto err_nlmsg_free;
> > 
> > Is it important to have an ability to fail here? Can we simply ignore
> > failure?
> 
> Should be fine.
> 
> Thanks