[LU-5569] recreating a reverse import produce a various fails.

Blocker — Fri, 15 Mar 2019 17:17:21 +0000

Don't reallocate a new reverse import for each client reconnect.
a reverse import disconnecting on each client reconnect open
several races in request sending (AST mostly) code.

First problem is send_rpc vs class_destroy_import() race. If sending
RPC (or resending) issued after class_destroy_import function was
called, RPC sending will failed due import generation check.

Second problem, Target_handle_connect function stop an update a
connection information for older reverse import. So RPC can't be
delivered from server to the client due wrong connection information
or security flavor changed.

Target_handle_connect function stops update connection information
for older reverse import. So we can't delivers a RPC from server to
the client due wrong connection information or security flavor
changed.

Third problem, connection flags aren't updates atomically for an
import. Target_handle_connect function does link new import before
message headers flags are set. So, RPC will have a wrong flags set
if it would be sent at the same time.

Fourth problem, client reconnecting after network flap have result
none wakeup event send to a RPC in import queues. That situation adds
noticeable timeout in case server don't send request before network
flap.

some examples

00000100:00100000:1.0:1407845348.937766:0:62024:0:(service.c:1929:ptlrpc_server_handle_request()) Handled RPC pname:cluuid+ref:pid:xid:nid:opc ll_ost_419:4960df0f-75ed-07a2-cee7-063090dc59cd+4:19257:x1475700821793316:12345-1748@gni1:8 Request procesed in 55us (106us total) trans 0 rc 0/0

00000100:00020000:1.0:1407845393.600747:0:81897:0:(client.c:1115:ptlrpc_import_delay_req()) @@@ req wrong generation:  req@ffff880304e39800 x1475078782385806/t0(0) o105->snx11063-OST0070@1748@gni1:15/16 lens 344/192 e 0 to 1 dl 1407845389 ref 1 fl Rpc:X/2/ffffffff rc 0/-1

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[LU-5569] recreating a reverse import produce a various fails.