[PATCH 7/7] blktrace: avoid accessing NULL bdev->bd_disk

[Li Zefan <lizf@cn.fujitsu.com>]

bdev->bd_disk can be NULL, if the block device is not opened.

Try this against an unmounted partition, and you'll see NULL dereference:
  # echo 1 > /sys/block/sda/sda5/enable

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 kernel/trace/blktrace.c |   13 +++++++++++--
 1 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 46e0cfe..37095d9 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -1362,6 +1362,14 @@ static int blk_str2act_mask(const char *str)
 	return mask;
 }
 
+static request_queue *blk_trace_get_queue(struct block_device *bdev)
+{
+	if (bdev->bd_disk == NULL)
+		return NULL;
+
+	return bdev_get_queue(bdev);
+}
+
 static ssize_t sysfs_blk_trace_attr_show(struct device *dev,
 					 struct device_attribute *attr,
 					 char *buf)
@@ -1376,9 +1384,10 @@ static ssize_t sysfs_blk_trace_attr_show(struct device *dev,
 	if (bdev == NULL)
 		goto out_unlock_kernel;
 
-	q = bdev_get_queue(bdev);
+	q = blk_trace_get_queue(bdev);
 	if (q == NULL)
 		goto out_bdput;
+
 	mutex_lock(&bdev->bd_mutex);
 
 	if (attr == &dev_attr_enable) {
@@ -1435,7 +1444,7 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
 	if (bdev == NULL)
 		goto out_unlock_kernel;
 
-	q = bdev_get_queue(bdev);
+	q = blk_trace_get_queue(bdev);
 	if (q == NULL)
 		goto out_bdput;
 
-- 
1.5.4.rc3