[S390] cio: fix parallel cm_enable processing.

It is now possible to trigger cm_enable processing several times in
parallel without causing a kernel panic.

Signed-off-by: Michael Ernst <mernst@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

drivers/s390/cio/chsc.c

@@ -766,7 +766,6 @@ chsc_secm(struct channel_subsystem *css, int enable)
 	if (!secm_area)
 		return -ENOMEM;
 
-	mutex_lock(&css->mutex);
 	if (enable && !css->cm_enabled) {
 		css->cub_addr1 = (void *)get_zeroed_page(GFP_KERNEL | GFP_DMA);
 		css->cub_addr2 = (void *)get_zeroed_page(GFP_KERNEL | GFP_DMA);
@@ -774,7 +773,6 @@ chsc_secm(struct channel_subsystem *css, int enable)
 			free_page((unsigned long)css->cub_addr1);
 			free_page((unsigned long)css->cub_addr2);
 			free_page((unsigned long)secm_area);
-			mutex_unlock(&css->mutex);
 			return -ENOMEM;
 		}
 	}
@@ -795,7 +793,6 @@ chsc_secm(struct channel_subsystem *css, int enable)
 		free_page((unsigned long)css->cub_addr1);
 		free_page((unsigned long)css->cub_addr2);
 	}
-	mutex_unlock(&css->mutex);
 	free_page((unsigned long)secm_area);
 	return ret;
 }

drivers/s390/cio/css.c

@@ -689,10 +689,14 @@ css_cm_enable_show(struct device *dev, struct device_attribute *attr,
 		   char *buf)
 {
 	struct channel_subsystem *css = to_css(dev);
+	int ret;
 
 	if (!css)
 		return 0;
-	return sprintf(buf, "%x\n", css->cm_enabled);
+	mutex_lock(&css->mutex);
+	ret = sprintf(buf, "%x\n", css->cm_enabled);
+	mutex_unlock(&css->mutex);
+	return ret;
 }
 
 static ssize_t
@@ -702,6 +706,7 @@ css_cm_enable_store(struct device *dev, struct device_attribute *attr,
 	struct channel_subsystem *css = to_css(dev);
 	int ret;
 
+	mutex_lock(&css->mutex);
 	switch (buf[0]) {
 	case '0':
 		ret = css->cm_enabled ? chsc_secm(css, 0) : 0;
@@ -712,6 +717,7 @@ css_cm_enable_store(struct device *dev, struct device_attribute *attr,
 	default:
 		ret = -EINVAL;
 	}
+	mutex_unlock(&css->mutex);
 	return ret < 0 ? ret : count;
 }
 
@@ -758,9 +764,11 @@ static int css_reboot_event(struct notifier_block *this,
 		struct channel_subsystem *css;
 
 		css = channel_subsystems[i];
+		mutex_lock(&css->mutex);
 		if (css->cm_enabled)
 			if (chsc_secm(css, 0))
 				ret = NOTIFY_BAD;
+		mutex_unlock(&css->mutex);
 	}
 
 	return ret;