Hi Kieran,
On Tue, Jan 16, 2018 at 02:52:58PM +0000, Kieran Bingham wrote:
> From: Kieran Bingham <[email protected]>
>
> It can be easy to attempt to register the same notifier twice
> in mis-handled error cases such as working with -EPROBE_DEFER.
>
> This results in odd kernel crashes where the notifier_list becomes
> corrupted due to adding the same entry twice.
>
> Protect against this so that a developer has some sense of the pending
> failure.
>
> Signed-off-by: Kieran Bingham <[email protected]>
> ---
> drivers/media/v4l2-core/v4l2-async.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/drivers/media/v4l2-core/v4l2-async.c
> b/drivers/media/v4l2-core/v4l2-async.c
> index 2b08d03b251d..e8476f0755ca 100644
> --- a/drivers/media/v4l2-core/v4l2-async.c
> +++ b/drivers/media/v4l2-core/v4l2-async.c
> @@ -374,6 +374,7 @@ static int __v4l2_async_notifier_register(struct
> v4l2_async_notifier *notifier)
> struct device *dev =
> notifier->v4l2_dev ? notifier->v4l2_dev->dev : NULL;
> struct v4l2_async_subdev *asd;
> + struct v4l2_async_notifier *n;
> int ret;
> int i;
>
> @@ -385,6 +386,19 @@ static int __v4l2_async_notifier_register(struct
> v4l2_async_notifier *notifier)
>
> mutex_lock(&list_lock);
>
> + /*
> + * Registering the same notifier can occur if a driver incorrectly
> + * handles a -EPROBE_DEFER for example, and will break in a
> + * confusing fashion with linked-list corruption.
> + */
This would seem fine in the commit message, and it's essentially there
already. How about simply:
/* Avoid re-registering a notifier. */
You should actually perform the check before initialising the notifier's
lists. Although things are likely in a quite bad shape already if this
happens.
> + list_for_each_entry(n, ¬ifier_list, list) {
> + if (n == notifier) {
if (WARN_ON(n == notifier)) {
And drop the error message below?
> + dev_err(dev, "Notifier has already been registered\n");
> + ret = -EEXIST;
> + goto err_unlock;
> + }
> + }
> +
> for (i = 0; i < notifier->num_subdevs; i++) {
> asd = notifier->subdevs[i];
>
--
Regards,
Sakari Ailus
e-mail: [email protected]
