RDMA/rxe: Fix a race condition related to the QP error state

BugLink: http://bugs.launchpad.net/bugs/1751131
commit 6f301e06de4cf9ab7303f5acd43e64fcd4aa04be upstream.

The following sequence:
* Change queue pair state into IB_QPS_ERR.
* Post a work request on the queue pair.

Triggers the following race condition in the rdma_rxe driver:
* rxe_qp_error() triggers an asynchronous call of rxe_completer(), the function
  that examines the QP send queue.
* rxe_post_send() posts a work request on the QP send queue.

If rxe_completer() runs prior to rxe_post_send(), it will drain the send
queue and the driver will assume no further action is necessary.
However, once we post the send to the send queue, because the queue is
in error, no send completion will ever happen and the send will get
stuck.  In order to process the send, we need to make sure that
rxe_completer() gets run after a send is posted to a queue pair in an
error state.  This patch ensures that happens.

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Moni Shoua <monis@mellanox.com>
Cc: <stable@vger.kernel.org> # v4.8
Signed-off-by: Doug Ledford <dledford@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

diff --git a/drivers/infiniband/sw/rxe/rxe_verbs.c b/drivers/infiniband/sw/rxe/rxe_verbs.c
index d03002b9d84de098460889206296ae7541b2388d..7210a784abb497cf89657024d3633d45f7c56cd9 100644 (file)
--- a/drivers/infiniband/sw/rxe/rxe_verbs.c
+++ b/drivers/infiniband/sw/rxe/rxe_verbs.c
@@ -814,6 +814,8 @@ static int rxe_post_send_kernel(struct rxe_qp *qp, struct ib_send_wr *wr,
                        (queue_count(qp->sq.queue) > 1);
 
        rxe_run_task(&qp->req.task, must_sched);
+       if (unlikely(qp->req.state == QP_STATE_ERROR))
+               rxe_run_task(&qp->comp.task, 1);
 
        return err;
 }