On Mon, Feb 06, 2017 at 01:41:39PM +1100, Neil Brown wrote:
>
>
> Commit: cbd199837750 ("md: Fix unfortunate interaction with evms")
> change mddev_put() so that it would not destroy an md device while
> ->ctime was non-zero.
>
> Unfortunately, we didn't make sure to clear ->ctime when unloading
> the module, so it is possible for an md device to remain after
> module unload. An attempt to open such a device will trigger
> an invalid memory reference in:
> get_gendisk -> kobj_lookup -> exact_lock -> get_disk
>
> when tring to access disk->fops, which was in the module that has
> been removed.
>
> So ensure we clear ->ctime in md_exit(), and explain how that is useful,
> as it isn't immediately obvious when looking at the code.
>
> Fixes: cbd199837750 ("md: Fix unfortunate interaction with evms")
> Tested-by: Guoqing Jiang <gqjiang@xxxxxxxx>
> Signed-off-by: NeilBrown <neilb@xxxxxxxx>
Applied, thanks!
> ---
> drivers/md/md.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 01175dac0db6..8926fb781cdc 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -8980,7 +8980,14 @@ static __exit void md_exit(void)
>
> for_each_mddev(mddev, tmp) {
> export_array(mddev);
> + mddev->ctime = 0;
> mddev->hold_active = 0;
> + /* for_each_mddev() will call mddev_put() at the
> + * end of each iteration. As the mddev is now
> + * fully clear, this will schedule the mddev for destruction
> + * by a workqueue, and the destroy_workqueue() below
> + * will wait for that to complete.
> + */
> }
> destroy_workqueue(md_misc_wq);
> destroy_workqueue(md_wq);
> --
> 2.11.0
>
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