RDMA/rxe: Fix null pointer dereference in ODP MR check

The blktests/rnbd reported a null pointer dereference as following.
Similar to the mlx5, introduce a is_odp_mr() to check if the odp is
enabled in this mr.

  Workqueue: rxe_wq do_work [rdma_rxe]
  RIP: 0010:rxe_mr_copy+0x57/0x210 [rdma_rxe]
  Code: 7c 04 48 89 f3 48 89 d5 41 89 cf 45 89 c4 0f 84 dc 00 00 00 89 ca e8 f8 f8 ff ff 85 c0 0f 85 75 01 00 00 49 8b 86 f0 00 00 00 <f6> 40 28 02 0f 85 98 01 00 00 41 8b 46 78 41 8b 8e 10 01 00 00 8d
  RSP: 0018:ffffa0aac02cfcf8 EFLAGS: 00010246
  RAX: 0000000000000000 RBX: ffff9079cd440024 RCX: 0000000000000000
  RDX: 000000000000003c RSI: ffff9079cd440060 RDI: ffff9079cd665600
  RBP: ffff9079c0e5e45a R08: 0000000000000000 R09: 0000000000000000
  R10: 000000003c000000 R11: 0000000000225510 R12: 0000000000000000
  R13: 0000000000000000 R14: ffff9079cd665600 R15: 000000000000003c
  FS:  0000000000000000(0000) GS:ffff907ccfa80000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000000000028 CR3: 0000000119498001 CR4: 00000000001726f0
  Call Trace:
   <TASK>
   ? __die_body+0x1e/0x60
   ? page_fault_oops+0x14f/0x4c0
   ? rxe_mr_copy+0x57/0x210 [rdma_rxe]
   ? search_bpf_extables+0x5f/0x80
   ? exc_page_fault+0x7e/0x180
   ? asm_exc_page_fault+0x26/0x30
   ? rxe_mr_copy+0x57/0x210 [rdma_rxe]
   ? rxe_mr_copy+0x48/0x210 [rdma_rxe]
   ? rxe_pool_get_index+0x50/0x90 [rdma_rxe]
   rxe_receiver+0x1d98/0x2530 [rdma_rxe]
   ? psi_task_switch+0x1ff/0x250
   ? finish_task_switch+0x92/0x2d0
   ? __schedule+0xbdf/0x17c0
   do_task+0x65/0x1e0 [rdma_rxe]
   process_scheduled_works+0xaa/0x3f0
   worker_thread+0x117/0x240

Fixes: d03fb5c ("RDMA/rxe: Allow registering MRs for On-Demand Paging")
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/r/20250402032657.1762800-1-lizhijian@fujitsu.com
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
Reviewed-by: Daisuke Matsuda <matsuda-daisuke@fujitsu.com>
Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Author: zhijianli88

drivers/infiniband/sw/rxe/rxe_loc.h

@@ -140,6 +140,12 @@ static inline int qp_mtu(struct rxe_qp *qp)
 		return IB_MTU_4096;
 }
 
+static inline bool is_odp_mr(struct rxe_mr *mr)
+{
+	return IS_ENABLED(CONFIG_INFINIBAND_ON_DEMAND_PAGING) && mr->umem &&
+	       mr->umem->is_odp;
+}
+
 void free_rd_atomic_resource(struct resp_res *res);
 
 static inline void rxe_advance_resp_resource(struct rxe_qp *qp)

drivers/infiniband/sw/rxe/rxe_mr.c

@@ -323,7 +323,7 @@ int rxe_mr_copy(struct rxe_mr *mr, u64 iova, void *addr,
 		return err;
 	}
 
-	if (mr->umem->is_odp)
+	if (is_odp_mr(mr))
 		return rxe_odp_mr_copy(mr, iova, addr, length, dir);
 	else
 		return rxe_mr_copy_xarray(mr, iova, addr, length, dir);
@@ -536,7 +536,7 @@ int rxe_mr_do_atomic_write(struct rxe_mr *mr, u64 iova, u64 value)
 	u64 *va;
 
 	/* ODP is not supported right now. WIP. */
-	if (mr->umem->is_odp)
+	if (is_odp_mr(mr))
 		return RESPST_ERR_UNSUPPORTED_OPCODE;
 
 	/* See IBA oA19-28 */

drivers/infiniband/sw/rxe/rxe_resp.c

@@ -650,7 +650,7 @@ static enum resp_states process_flush(struct rxe_qp *qp,
 	struct resp_res *res = qp->resp.res;
 
 	/* ODP is not supported right now. WIP. */
-	if (mr->umem->is_odp)
+	if (is_odp_mr(mr))
 		return RESPST_ERR_UNSUPPORTED_OPCODE;
 
 	/* oA19-14, oA19-15 */
@@ -706,7 +706,7 @@ static enum resp_states atomic_reply(struct rxe_qp *qp,
 	if (!res->replay) {
 		u64 iova = qp->resp.va + qp->resp.offset;
 
-		if (mr->umem->is_odp)
+		if (is_odp_mr(mr))
 			err = rxe_odp_atomic_op(mr, iova, pkt->opcode,
 						atmeth_comp(pkt),
 						atmeth_swap_add(pkt),