tree 2cef8cc9855b9e5e97c0aa9f65f091c4d4e55f3b
parent eea63ca7ffa1f3a4a0b02b902ec51eab2d4e9df4
author Chuck Lever <chuck.lever@oracle.com> 1570640858 -0400
committer Anna Schumaker <Anna.Schumaker@Netapp.com> 1571927440 -0400

xprtrdma: Close window between waking RPC senders and posting Receives

A recent clean up attempted to separate Receive handling and RPC
Reply processing, in the name of clean layering.

Unfortunately, we can't do this because the Receive Queue has to be
refilled _after_ the most recent credit update from the responder
is parsed from the transport header, but _before_ we wake up the
next RPC sender. That is right in the middle of
rpcrdma_reply_handler().

Usually this isn't a problem because current responder
implementations don't vary their credit grant. The one exception is
when a connection is established: the grant goes from one to a much
larger number on the first Receive. The requester MUST post enough
Receives right then so that any outstanding requests can be sent
without risking RNR and connection loss.

Fixes: 6ceea36890a0 ("xprtrdma: Refactor Receive accounting")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>