Re: [PATCH rdma-next] Revert "IB/core: Add flow control to the portmapper netlink calls"
From: Doug Ledford <hidden>
Date: 2017-06-05 14:27:47
On Fri, 2017-06-02 at 11:28 -0500, Shiraz Saleem wrote:
On Wed, May 31, 2017 at 02:10:31PM -0600, Bart Van Assche wrote:quoted
On Wed, 2017-05-31 at 12:42 -0500, Shiraz Saleem wrote:quoted
quoted
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.
Just to be clear, replacing a non-blocking and occasionally dropping function with a blocking function but with a timeout does not actually solve the problem, it merely moves the goal post out. It is entirely possible that you will have the problem again given sufficient load. -- Doug Ledford [off-list ref] GPG KeyID: B826A3330E572FDD Key fingerprint = AE6B 1BDA 122B 23B4 265B 1274 B826 A333 0E57 2FDD -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html