sgi-xp: incoming XPC channel messages can come in after the channel's partition structures have been torn down

Under some workloads, some channel messages have been observed being
delayed on the sending side past the point where the receiving side has
been able to tear down its partition structures.

This condition is already detected in xpc_handle_activate_IRQ_uv(), but
that information is not given to xpc_handle_activate_mq_msg_uv(). As a
result, xpc_handle_activate_mq_msg_uv() assumes the structures still exist
and references them, causing a NULL-pointer deref.

Signed-off-by: Robin Holt <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/misc/sgi-xp/xpc_uv.c

···
 static void
 xpc_handle_activate_mq_msg_uv(struct xpc_partition *part,
 			      struct xpc_activate_mq_msghdr_uv *msg_hdr,
+			      int part_setup,
 			      int *wakeup_hb_checker)
 {
 	unsigned long irq_flags;
···
 	case XPC_ACTIVATE_MQ_MSG_CHCTL_CLOSEREQUEST_UV: {
 		struct xpc_activate_mq_msg_chctl_closerequest_uv *msg;
 
+		if (!part_setup)
+			break;
+
 		msg = container_of(msg_hdr, struct
 				   xpc_activate_mq_msg_chctl_closerequest_uv,
 				   hdr);
···
 	case XPC_ACTIVATE_MQ_MSG_CHCTL_CLOSEREPLY_UV: {
 		struct xpc_activate_mq_msg_chctl_closereply_uv *msg;
 
+		if (!part_setup)
+			break;
+
 		msg = container_of(msg_hdr, struct
 				   xpc_activate_mq_msg_chctl_closereply_uv,
 				   hdr);
···
 	}
 	case XPC_ACTIVATE_MQ_MSG_CHCTL_OPENREQUEST_UV: {
 		struct xpc_activate_mq_msg_chctl_openrequest_uv *msg;
+
+		if (!part_setup)
+			break;
 
 		msg = container_of(msg_hdr, struct
 				   xpc_activate_mq_msg_chctl_openrequest_uv,
···
 	case XPC_ACTIVATE_MQ_MSG_CHCTL_OPENREPLY_UV: {
 		struct xpc_activate_mq_msg_chctl_openreply_uv *msg;
 
+		if (!part_setup)
+			break;
+
 		msg = container_of(msg_hdr, struct
 				   xpc_activate_mq_msg_chctl_openreply_uv, hdr);
 		args = &part->remote_openclose_args[msg->ch_number];
···
 	}
 	case XPC_ACTIVATE_MQ_MSG_CHCTL_OPENCOMPLETE_UV: {
 		struct xpc_activate_mq_msg_chctl_opencomplete_uv *msg;
+
+		if (!part_setup)
+			break;
 
 		msg = container_of(msg_hdr, struct
 				xpc_activate_mq_msg_chctl_opencomplete_uv, hdr);
···
 
 			part_referenced = xpc_part_ref(part);
 			xpc_handle_activate_mq_msg_uv(part, msg_hdr,
+						      part_referenced,
 						      &wakeup_hb_checker);
 			if (part_referenced)
 				xpc_part_deref(part);