From: Hans-Joachim Picht <hpicht@redhat.com>
Date: Tue, 29 Sep 2009 22:43:29 +0200
Subject: [s390] cio: boot through XAUTOLOG with conmode 3270
Message-id: 20090929204329.GA26546@blc4eb509856389.ibm.com
O-Subject: [RHEL5 U5 PATCH 1/1] s390 - cio: Linux does not boot through XAUTOLOG with conmode 3270
Bugzilla: 508934
RH-Acked-by: Pete Zaitcev <zaitcev@redhat.com>
RH-Acked-by: Jiri Olsa <jolsa@redhat.com>
RH-Acked-by: Jiri Pirko <jpirko@redhat.com>

Description
===========
The system does not boot through CP XAUTOLOG with conmode= set to 3270.

The problem is caused by writing debug data to an uninitialized debug feature
that results in a never ending loop.  To solve this issue, only write debug
data to an initialized debug feature.

Bugzilla
========

BZ 508934
https://bugzilla.redhat.com/show_bug.cgi?id=508934

Upstream status of the patch
============================

The patch is upstream as of kernel version 2.6.23

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=303fa9e39605c1d56971dd22cd04d2186dc42c98

Test status
===========

The patch has been tested and fixes the problem.
The fix has been verified by the IBM test department.

Please ACK.

With best regards,

	Hans

diff --git a/drivers/s390/cio/cio_debug.h b/drivers/s390/cio/cio_debug.h
index f88844a..c9bf898 100644
--- a/drivers/s390/cio/cio_debug.h
+++ b/drivers/s390/cio/cio_debug.h
@@ -23,6 +23,8 @@ extern debug_info_t *cio_debug_crw_id;
 static inline void
 CIO_HEX_EVENT(int level, void *data, int length)
 {
+	if (unlikely(!cio_debug_trace_id))
+		return;
 	while (length > 0) {
 		debug_event(cio_debug_trace_id, level, data, length);
 		length -= cio_debug_trace_id->buf_size;