IB/rxe: Fix handling of erroneous WR

To correctly handle a erroneous WR this fix does the following
1. Make sure the bad WQE causes a user completion event.
2. Call rxe_completer to handle the erred WQE.

Before the fix, when rxe_requester found a bad WQE, it changed its
status to IB_WC_LOC_PROT_ERR and exit with 0 for non RC QPs.

If this was the 1st WQE then there would be no ACK to invoke the
completer and this bad WQE would be stuck in the QP's send-q.

On top of that the requester exiting with 0 caused rxe_do_task to
endlessly invoke rxe_requester, resulting in a soft-lockup attached
below.

In case the WQE was not the 1st and rxe_completer did get a chance to
handle the bad WQE, it did not cause a complete event since the WQE's
IB_SEND_SIGNALED flag was not set.

Setting WQE status to IB_SEND_SIGNALED is subject to IBA spec
version 1.2.1, section 10.7.3.1 Signaled Completions.

NMI watchdog: BUG: soft lockup - CPU#7 stuck for 22s!
[<ffffffffa0590145>] ? rxe_pool_get_index+0x35/0xb0 [rdma_rxe]
[<ffffffffa05952ec>] lookup_mem+0x3c/0xc0 [rdma_rxe]
[<ffffffffa0595534>] copy_data+0x1c4/0x230 [rdma_rxe]
[<ffffffffa058c180>] rxe_requester+0x9d0/0x1100 [rdma_rxe]
[<ffffffff8158e98a>] ? kfree_skbmem+0x5a/0x60
[<ffffffffa05962c9>] rxe_do_task+0x89/0xf0 [rdma_rxe]
[<ffffffffa05963e2>] rxe_run_task+0x12/0x30 [rdma_rxe]
[<ffffffffa059110a>] rxe_post_send+0x41a/0x550 [rdma_rxe]
[<ffffffff811ef922>] ? __kmalloc+0x182/0x200
[<ffffffff816ba512>] ? down_read+0x12/0x40
[<ffffffffa054bd32>] ib_uverbs_post_send+0x532/0x540 [ib_uverbs]
[<ffffffff815f8722>] ? tcp_sendmsg+0x402/0xb80
[<ffffffffa05453dc>] ib_uverbs_write+0x18c/0x3f0 [ib_uverbs]
[<ffffffff81623c2e>] ? inet_recvmsg+0x7e/0xb0
[<ffffffff8158764d>] ? sock_recvmsg+0x3d/0x50
[<ffffffff81215b87>] __vfs_write+0x37/0x140
[<ffffffff81216892>] vfs_write+0xb2/0x1b0
[<ffffffff81217ce5>] SyS_write+0x55/0xc0
[<ffffffff816bc672>] entry_SYSCALL_64_fastpath+0x1a/0xa

Fixes: 8700e3e7c485 ("Soft RoCE driver")
Signed-off-by: Yonatan Cohen <yonatanc@mellanox.com>
Reviewed-by: Moni Shoua <monis@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/sw/rxe/rxe_req.c

@@ -696,7 +696,8 @@ next_wqe:
 						       qp->req.wqe_index);
 			wqe->state = wqe_state_done;
 			wqe->status = IB_WC_SUCCESS;
-			goto complete;
+			__rxe_do_task(&qp->comp.task);
+			return 0;
 		}
 		payload = mtu;
 	}
@@ -745,13 +746,17 @@ err:
 	wqe->status = IB_WC_LOC_PROT_ERR;
 	wqe->state = wqe_state_error;
 
-complete:
-	if (qp_type(qp) != IB_QPT_RC) {
-		while (rxe_completer(qp) == 0)
-			;
-	}
-
-	return 0;
+	/*
+	 * IBA Spec. Section 10.7.3.1 SIGNALED COMPLETIONS
+	 * ---------8<---------8<-------------
+	 * ...Note that if a completion error occurs, a Work Completion
+	 * will always be generated, even if the signaling
+	 * indicator requests an Unsignaled Completion.
+	 * ---------8<---------8<-------------
+	 */
+	wqe->wr.send_flags |= IB_SEND_SIGNALED;
+	__rxe_do_task(&qp->comp.task);
+	return -EAGAIN;
 
 exit:
 	return -EAGAIN;