[PATCH 1/3] s390/cio: Fix cio_update_schib() to not cache invalid schib

[Vineeth Vijayan <vneethv@linux.ibm.com>]

When pmcw.dnv is 0, the contents of all SCHIB fields are unpredictable.
Zero sch->schib in that case to prevent subsequent code from making
decisions based on unpredictable data.

Reported-by: William Bezenah <wbezenah@linux.ibm.com>
Signed-off-by: Vineeth Vijayan <vneethv@linux.ibm.com>
Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Fixes: 8c58a229688c ("s390/cio: Do not unregister the subchannel based on DNV")
---
 drivers/s390/cio/cio.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/s390/cio/cio.c b/drivers/s390/cio/cio.c
index 70dc8cc76594..e1c62eb60cca 100644
--- a/drivers/s390/cio/cio.c
+++ b/drivers/s390/cio/cio.c
@@ -453,7 +453,8 @@ EXPORT_SYMBOL_GPL(cio_commit_config);
 /**
  * cio_update_schib - Perform stsch and update schib if subchannel is valid.
  * @sch: subchannel on which to perform stsch
- * Return zero on success, -ENODEV otherwise.
+ * Return zero on success, -ENODEV if the subchannel is not operational,
+ * -EACCES if the subchannel has no valid device.
  */
 int cio_update_schib(struct subchannel *sch)
 {
@@ -462,10 +463,12 @@ int cio_update_schib(struct subchannel *sch)
 	if (stsch(sch->schid, &schib))
 		return -ENODEV;
 
-	memcpy(&sch->schib, &schib, sizeof(schib));
-
-	if (!css_sch_is_valid(&schib))
+	if (!css_sch_is_valid(&schib)) {
+		memset(&sch->schib, 0, sizeof(sch->schib));
 		return -EACCES;
+	}
+
+	memcpy(&sch->schib, &schib, sizeof(schib));
 
 	return 0;
 }
-- 
2.53.0