[S390] sclp: handle empty event buffers

Handle a malformed hardware response which some versions of the
Support Element (SE) may present during SE restart and which otherwise
would result in an endless loop in function sclp_dispatch_evbufs.

Signed-off-by: Peter Oberparleiter <[e-mail]>
Signed-off-by: Martin Schwidefsky <[e-mail]>

drivers/s390/char/sclp.c

···
 	rc = 0;
 	for (offset = sizeof(struct sccb_header); offset < sccb->length;
 	     offset += evbuf->length) {
-		/* Search for event handler */
 		evbuf = (struct evbuf_header *) ((addr_t) sccb + offset);
+		/* Check for malformed hardware response */
+		if (evbuf->length == 0)
+			break;
+		/* Search for event handler */
 		reg = NULL;
 		list_for_each(l, &sclp_reg_list) {
 			reg = list_entry(l, struct sclp_register, list);