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    Subject[tip:tracing/blktrace] blktrace: avoid accessing NULL bdev->bd_disk
    Commit-ID:  afaebb6720cc62df1b03e36c2f699b00cfee784e
    Gitweb: http://git.kernel.org/tip/afaebb6720cc62df1b03e36c2f699b00cfee784e
    Author: Li Zefan <lizf@cn.fujitsu.com>
    AuthorDate: Fri, 20 Mar 2009 10:34:00 +0800
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Fri, 20 Mar 2009 11:20:07 +0100

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


    ---
    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 dfee6f9..108f4f7 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;


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