From 7c6553d4db03350dad0110c3224194c19df76a8f Mon Sep 17 00:00:00 2001
From: Stefan Haberland <sth@linux.ibm.com>
Date: Wed, 25 Jul 2018 13:27:10 +0200
Subject: [PATCH] s390/dasd: fix panic for failed online processing

References: bsc#1132589
Patch-mainline: v4.19-rc1
Git-commit: 7c6553d4db03350dad0110c3224194c19df76a8f

Description:   dasd: panic during online processing
Symptom:       Kernel may panic if online proccessing fails.
Problem:       While reading configuration data an I/O error may occur which
               causes the online processing to roll back all previous steps.
               A valid pointer for the private data structure of a device is
               expected when disconnecting the device from an lcu. However,
               if the I/O error occurs very early, the private data structure
               hasn't been set up yet. An invalid pointer is the result and
               causes the kernel to panic.
Solution:      Check for a valid private data pointer before disconnecting a
               device from the lcu.
Reproduction:  While turning all CHPIDs for a DASD off/on with chchp -v 0/1
               and then setting the same DASD online (chccwdev -e <device>) can
               reproduce the issue. The pathgroup may get lost and the online
               processing will fail early, causing the access of an invalid
               pointer.

Fix a panic that occurs for a device that got an error in
dasd_eckd_check_characteristics() during online processing.
For example the read configuration data command may have failed.

If this error occurs the device is not being set online and the earlier
invoked steps during online processing are rolled back. Therefore
dasd_eckd_uncheck_device() is called which needs a valid private
structure. But this pointer is not valid if
dasd_eckd_check_characteristics() has failed.

Check for a valid device->private pointer to prevent a panic.

Reviewed-by: Jan Hoeppner <hoeppner@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 drivers/s390/block/dasd_eckd.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/s390/block/dasd_eckd.c b/drivers/s390/block/dasd_eckd.c
index c5a55513b07c..1e97378d4f60 100644
--- a/drivers/s390/block/dasd_eckd.c
+++ b/drivers/s390/block/dasd_eckd.c
@@ -1780,6 +1780,9 @@ static void dasd_eckd_uncheck_device(struct dasd_device *device)
 	struct dasd_eckd_private *private = device->private;
 	int i;
 
+	if (!private)
+		return;
+
 	dasd_alias_disconnect_device_from_lcu(device);
 	private->ned = NULL;
 	private->sneq = NULL;
-- 
2.20.1