blktrace: avoid accessing NULL bdev->bd_disk

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>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <49C30098.6080107@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 11 insertions, 2 deletions

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index dfee6f915179..108f4f7715a5 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 struct 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;