1 files changed, 18 insertions, 8 deletions

diff --git a/drivers/s390/cio/ccwgroup.c b/drivers/s390/cio/ccwgroup.c
index 3ac2c2019f5e..918e6fce2573 100644
--- a/drivers/s390/cio/ccwgroup.c
+++ b/drivers/s390/cio/ccwgroup.c
@@ -19,6 +19,8 @@
 #include <asm/ccwdev.h>
 #include <asm/ccwgroup.h>
 
+#define CCW_BUS_ID_SIZE		20
+
 /* In Linux 2.4, we had a channel device layer called "chandev"
  * that did all sorts of obscure stuff for networking devices.
  * This is another driver that serves as a replacement for just
@@ -89,15 +91,23 @@ ccwgroup_ungroup_store(struct device *dev, struct device_attribute *attr, const
 
 	gdev = to_ccwgroupdev(dev);
 
-	if (gdev->state != CCWGROUP_OFFLINE)
-		return -EINVAL;
-
+	/* Prevent concurrent online/offline processing and ungrouping. */
+	if (atomic_cmpxchg(&gdev->onoff, 0, 1) != 0)
+		return -EAGAIN;
+	if (gdev->state != CCWGROUP_OFFLINE) {
+		rc = -EINVAL;
+		goto out;
+	}
 	/* Note that we cannot unregister the device from one of its
 	 * attribute methods, so we have to use this roundabout approach.
 	 */
 	rc = device_schedule_callback(dev, ccwgroup_ungroup_callback);
-	if (rc)
-		count = rc;
+out:
+	if (rc) {
+		/* Release onoff "lock" when ungrouping failed. */
+		atomic_set(&gdev->onoff, 0);
+		return rc;
+	}
 	return count;
 }
 
@@ -172,7 +182,7 @@ static int __get_next_bus_id(const char **buf, char *bus_id)
 		len = end - start + 1;
 		end++;
 	}
-	if (len < BUS_ID_SIZE) {
+	if (len < CCW_BUS_ID_SIZE) {
 		strlcpy(bus_id, start, len);
 		rc = 0;
 	} else
@@ -181,7 +191,7 @@ static int __get_next_bus_id(const char **buf, char *bus_id)
 	return rc;
 }
 
-static int __is_valid_bus_id(char bus_id[BUS_ID_SIZE])
+static int __is_valid_bus_id(char bus_id[CCW_BUS_ID_SIZE])
 {
 	int cssid, ssid, devno;
 
@@ -213,7 +223,7 @@ int ccwgroup_create_from_string(struct device *root, unsigned int creator_id,
 {
 	struct ccwgroup_device *gdev;
 	int rc, i;
-	char tmp_bus_id[BUS_ID_SIZE];
+	char tmp_bus_id[CCW_BUS_ID_SIZE];
 	const char *curr_buf;
 
 	gdev = kzalloc(sizeof(*gdev) + num_devices * sizeof(gdev->cdev[0]),