Re: [PATCH] Fix: Remove racy Subnet Manager sendonly join checks

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Jan 28, 2021 at 02:58:01PM +0000, Christoph Lameter wrote:
> On Thu, 28 Jan 2021, Jason Gunthorpe wrote:
> 
> > > Well it was quilt ...... Do I need to put it into a git tree somewhere?
> >
> > If you are doing this a lot get a quilt that can generate git diff
> > format output.
> >
> > https://lists.gnu.org/archive/html/quilt-dev/2015-06/msg00002.html
> 
> Sadly that patch was never merged.
> 
> Will this do it?

Patchworks ingored it

> 
> commit 64e734c38f509d591073fc1e1db3caa42be3b874
> Author: Christoph Lameter <cl@linux.com>
> Date:   Thu Jan 28 14:55:36 2021 +0000
> 
>     Fix: Remove racy Subnet Manager sendonly join checks
> 
>     When a system receives a REREG event from the SM, then the SM information in
>     the kernel is marked as invalid and a request is sent to the SM to update
>     the information. The SM information is invalid in that time period.
> 
>     However, receiving a REREG also occurs simultaneously in user space
>     applications that are now trying to rejoin the multicast groups. Some of those
>     may be sendonly multicast groups which are then failing.
> 
>     If the SM information is invalid then ib_sa_sendonly_fullmem_support()
>     returns false. That is wrong because it just means that we do not know
>     yet if the potentially new SM supports sendonly joins.
> 
>     Sendonly join was introduced in 2015 and all the Subnet managers have
>     supported it ever since. So there is no point in checking if a subnet
>     manager supports it.
> 
>     Should an old opensm get a request for a sendonly join then the request
>     will fail. The code that is removed here accomodated that situation
>     and fell back to a full join.
> 
>     Falling back to a full join is problematic in itself. The reason to
>     use the sendonly join was to reduce the traffic on the Infiniband
>     fabric otherwise one could have just stayed with the regular join.
>     So this patch may cause users of very old opensms to discover that
>     lots of traffic needlessly crosses their IB fabrics.
> 
>     Signed-off-by: Christoph Lameter <cl@linux.com>

This is 'git show', not 'git format-patch', tooling requires 'git
format-patch' output. Preferably in a clean new email to get reliably
captured by patchworks

> diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c
> index c51b84b2d2f3..58ee7004c8d8 100644
> +++ b/drivers/infiniband/core/cma.c

But this is all OK now, the index line is what allows easy resolving
conflicts

Jason