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

Shiraz Saleem
2017-06-02T16:28:49Z

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.