Re: [PATCH] xprtrdma: make sure MRs are unmapped before freeing them

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On Fri, Aug 14, 2020 at 04:21:54PM -0400, Chuck Lever wrote:
> 
> 
> > On Aug 14, 2020, at 3:10 PM, Dan Aloni <dan@xxxxxxxxxxxx> wrote:
> > 
> > On Fri, Aug 14, 2020 at 02:12:48PM -0400, Chuck Lever wrote:
> >> Hi Dan-
> >> 
> >>> On Aug 14, 2020, at 1:37 PM, Dan Aloni <dan@xxxxxxxxxxxx> wrote:
> >>> 
> >>> It was observed that on disconnections, these unmaps don't occur. The
> >>> relevant path is rpcrdma_mrs_destroy(), being called from
> >>> rpcrdma_xprt_disconnect().
> >> 
> >> MRs are supposed to be unmapped right after they are used, so
> >> during disconnect they should all be unmapped already. How often
> >> do you see a DMA mapped MR in this code path? Do you have a
> >> reproducer I can try?
> > 
> > These are not graceful disconnections but abnormal ones, where many large
> > IOs are still in flight, while the remote server suddenly breaks the
> > connection, the remote IP is still reachable but refusing to accept new
> > connections only for a few seconds.
> 
> Ideally that's not supposed to matter. I'll see if I can reproduce
> with my usual tricks.
> 
> Why is your server behaving this way?

It's a dedicated storage cluster under a specific testing scenario,
implementing floating IPs.  Haven't tried, but maybe the same scenario
can be reproduced with a standard single Linux NFSv3 server by fiddling
with nfsd open ports.

-- 
Dan Aloni



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