IB/core: correctly handle rdma_rw_init_mrs() failure

Function ib_create_qp() was failing to return an error when
rdma_rw_init_mrs() fails, causing a crash further down in ib_create_qp()
when trying to dereferece the qp pointer which was actually a negative
errno.

The crash:

crash> log|grep BUG
[  136.458121] BUG: unable to handle kernel NULL pointer dereference at 0000000000000098
crash> bt
PID: 3736   TASK: ffff8808543215c0  CPU: 2   COMMAND: "kworker/u64:2"
 #0 [ffff88084d323340] machine_kexec at ffffffff8105fbb0
 Freescale#1 [ffff88084d3233b0] __crash_kexec at ffffffff81116758
 Freescale#2 [ffff88084d323480] crash_kexec at ffffffff8111682d
 Freescale#3 [ffff88084d3234b0] oops_end at ffffffff81032bd6
 Freescale#4 [ffff88084d3234e0] no_context at ffffffff8106e431
 Freescale#5 [ffff88084d323530] __bad_area_nosemaphore at ffffffff8106e610
 Freescale#6 [ffff88084d323590] bad_area_nosemaphore at ffffffff8106e6f4
 Freescale#7 [ffff88084d3235a0] __do_page_fault at ffffffff8106ebdc
 Freescale#8 [ffff88084d323620] do_page_fault at ffffffff8106f057
 Freescale#9 [ffff88084d323660] page_fault at ffffffff816e3148
    [exception RIP: ib_create_qp+427]
    RIP: ffffffffa02554fb  RSP: ffff88084d323718  RFLAGS: 00010246
    RAX: 0000000000000004  RBX: fffffffffffffff4  RCX: 000000018020001f
    RDX: ffff880830997fc0  RSI: 0000000000000001  RDI: ffff88085f407200
    RBP: ffff88084d323778   R8: 0000000000000001   R9: ffffea0020bae210
    R10: ffffea0020bae218  R11: 0000000000000001  R12: ffff88084d3237c8
    R13: 00000000fffffff4  R14: ffff880859fa5000  R15: ffff88082eb89800
    ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
Freescale#10 [ffff88084d323780] rdma_create_qp at ffffffffa0782681 [rdma_cm]
Freescale#11 [ffff88084d3237b0] nvmet_rdma_create_queue_ib at ffffffffa07c43f3 [nvmet_rdma]
Freescale#12 [ffff88084d323860] nvmet_rdma_alloc_queue at ffffffffa07c5ba9 [nvmet_rdma]
Freescale#13 [ffff88084d323900] nvmet_rdma_queue_connect at ffffffffa07c5c96 [nvmet_rdma]
Freescale#14 [ffff88084d323980] nvmet_rdma_cm_handler at ffffffffa07c6450 [nvmet_rdma]
Freescale#15 [ffff88084d3239b0] iw_conn_req_handler at ffffffffa0787480 [rdma_cm]
Freescale#16 [ffff88084d323a60] cm_conn_req_handler at ffffffffa0775f06 [iw_cm]
Freescale#17 [ffff88084d323ab0] process_event at ffffffffa0776019 [iw_cm]
Freescale#18 [ffff88084d323af0] cm_work_handler at ffffffffa0776170 [iw_cm]
Freescale#19 [ffff88084d323cb0] process_one_work at ffffffff810a1483
Freescale#20 [ffff88084d323d90] worker_thread at ffffffff810a211d
Freescale#21 [ffff88084d323ec0] kthread at ffffffff810a6c5c
Freescale#22 [ffff88084d323f50] ret_from_fork at ffffffff816e1ebf

Fixes: 632bc3f ("IB/core, RDMA RW API: Do not exceed QP SGE send limit")
Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Cc: stable@vger.kernel.org
Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/core/verbs.c

@@ -843,7 +843,7 @@ struct ib_qp *ib_create_qp(struct ib_pd *pd,
 		if (ret) {
 			pr_err("failed to init MR pool ret= %d\n", ret);
 			ib_destroy_qp(qp);
-			qp = ERR_PTR(ret);
+			return ERR_PTR(ret);
 		}
 	}