Re: [PATCH rdma-next] Revert "IB/core: Add flow control to the portmapper netlink calls"

[Leon Romanovsky <leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

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On Fri, Jun 02, 2017 at 11:28:49AM -0500, Shiraz Saleem wrote:
> On Wed, May 31, 2017 at 02:10:31PM -0600, Bart Van Assche wrote:
> > On Wed, 2017-05-31 at 12:42 -0500, Shiraz Saleem wrote:
> > > > 5. I proposed a solution -> go and fix your user space program.
> > >
> > > This is a kernel patch you are trying to revert, you are breaking existing
> > > kernel functionality.  Nothing to do with user space.
> > >
> > > Bottom line, come up with a solution that will address both port mapper
> > > functionality and your issue.
> >
> > Hello Shiraz,
> >
> > Sorry that this means additional work for you, but I agree with Leon that
> > user space software should not assume that netlink sockets are a reliable
> > communication mechanism.
>
> Hi Bart - Thank you for your response.
>
> The original problem was that ibnl_unicast, which is used to send nl messages from
> portmapper kernel space to user-space, would occasionally and momentarily fail under stress.
> We could have retried the call for a certain amount of time, but since netlink_unicast has a
> nonblock/block parameter, we chose to use the blocking option with a timeout. So we thought we
> did account for deadlocks with this timeout.

Not really, you just reduced the chances. In very large scale, you will
have a very large chances of such deadlocks.

Thanks

>
>
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