Re: [PATCH 3/5] hwrng: core - Do not register device opportunistically

Rusty Russell
2014-12-26T00:31:34Z

Herbert Xu <herbert@gondor.apana.org.au> writes:
> Currently we only register the device when a valid RNG is added.
> However the way it's done is buggy because we test whether there
> is a current RNG to determine whether we need to register. As
> the current RNG may be missing due to a reinitialisation error
> this can lead to a reregistration of the device.
>
> As the device already has to handle a NULL current RNG anyway,
> let's just register the device always and remove the complexity.

Does this break userspace by creating a device which will just return
-ENODEV on read? Sure, callers *should* handle it...

I far prefer this (simpler) model, though.

Thanks,
Rusty.

>
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
> ---
>
> drivers/char/hw_random/core.c | 23 ++++++++++++-----------
> 1 file changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> index 42827fd..1d342f0 100644
> --- a/drivers/char/hw_random/core.c
> +++ b/drivers/char/hw_random/core.c
> @@ -372,14 +372,14 @@ static DEVICE_ATTR(rng_available, S_IRUGO,
> NULL);
>
>
> -static void unregister_miscdev(void)
> +static void __exit unregister_miscdev(void)
> {
> device_remove_file(rng_miscdev.this_device, &dev_attr_rng_available);
> device_remove_file(rng_miscdev.this_device, &dev_attr_rng_current);
> misc_deregister(&rng_miscdev);
> }
>
> -static int register_miscdev(void)
> +static int __init register_miscdev(void)
> {
> int err;
>
> @@ -484,12 +484,6 @@ int hwrng_register(struct hwrng *rng)
> if (err)
> goto out_unlock;
> set_current_rng(rng);
> -
> - err = register_miscdev();
> - if (err) {
> - drop_current_rng();
> - goto out_unlock;
> - }
> }
> list_add_tail(&rng->list, &rng_list);
>
> @@ -530,7 +524,6 @@ void hwrng_unregister(struct hwrng *rng)
>
> if (list_empty(&rng_list)) {
> mutex_unlock(&rng_mutex);
> - unregister_miscdev();
> if (hwrng_fill)
> kthread_stop(hwrng_fill);
> } else
> @@ -540,16 +533,24 @@ void hwrng_unregister(struct hwrng *rng)
> }
> EXPORT_SYMBOL_GPL(hwrng_unregister);
>
> -static void __exit hwrng_exit(void)
> +static int __init hwrng_modinit(void)
> +{
> + return register_miscdev();
> +}
> +
> +static void __exit hwrng_modexit(void)
> {
> mutex_lock(&rng_mutex);
> BUG_ON(current_rng);
> kfree(rng_buffer);
> kfree(rng_fillbuf);
> mutex_unlock(&rng_mutex);
> +
> + unregister_miscdev();
> }
>
> -module_exit(hwrng_exit);
> +module_init(hwrng_modinit);
> +module_exit(hwrng_modexit);
>
> MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
> MODULE_LICENSE("GPL");