staging: lustre: ptlrpc: race at req processing

Fix: 5c689e68 ("staging/lustre/ptlrpc: race at req processing")
decreased the race window, but does not remove it. Disable rq_resend
right after MSG_REPLAY flag set. Import lock protects two threads
from race between set/clear MSG_REPLAY and rq_resend flags.
Signed-off-by: Alexander Boyko <alexander_boyko@xyratex.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5554
Xyratex-bug-id: MRP-1888
Reviewed-on: http://review.whamcloud.com/10735Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/ptlrpc/client.c

@@ -2714,6 +2714,10 @@ void ptlrpc_retain_replayable_request(struct ptlrpc_request *req,
 
 	lustre_msg_add_flags(req->rq_reqmsg, MSG_REPLAY);
 
+	spin_lock(&req->rq_lock);
+	req->rq_resend = 0;
+	spin_unlock(&req->rq_lock);
+
 	LASSERT(imp->imp_replayable);
 	/* Balanced in ptlrpc_free_committed, usually. */
 	ptlrpc_request_addref(req);