[PATCH] hwrng: Explicitly drop current_rng when unregistering rng device

[PATCH] hwrng: Explicitly drop current_rng when unregistering rng device

[Keith Packard]

When the currently in-use hw rng is being removed from the system,
explicitly drop it before using enable_best_rng as enable_best_rng
will not do anything if the list of avaialble RNGs is empty.

Without this, the last RNG removed from the system will never get
cleaned up and hwrng_unregister will hang.

Signed-off-by: Keith Packard <keithp@keithp.com>
---
 drivers/char/hw_random/core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 657b8770b6b9..8df3f9f147e2 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -515,8 +515,10 @@ void hwrng_unregister(struct hwrng *rng)
 	mutex_lock(&rng_mutex);
 
 	list_del(&rng->list);
-	if (current_rng == rng)
+	if (current_rng == rng) {
+		drop_current_rng();
 		enable_best_rng();
+	}
 
 	if (list_empty(&rng_list)) {
 		mutex_unlock(&rng_mutex);
-- 
2.15.1

Re: [PATCH] hwrng: Explicitly drop current_rng when unregistering rng device

[Tom Lendacky]

On 1/30/2018 5:26 PM, Keith Packard wrote:
> When the currently in-use hw rng is being removed from the system,
> explicitly drop it before using enable_best_rng as enable_best_rng
> will not do anything if the list of avaialble RNGs is empty.
> 
> Without this, the last RNG removed from the system will never get
> cleaned up and hwrng_unregister will hang.
> 
> Signed-off-by: Keith Packard <keithp@keithp.com>
> ---
>  drivers/char/hw_random/core.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> index 657b8770b6b9..8df3f9f147e2 100644
> --- a/drivers/char/hw_random/core.c
> +++ b/drivers/char/hw_random/core.c
> @@ -515,8 +515,10 @@ void hwrng_unregister(struct hwrng *rng)
>  	mutex_lock(&rng_mutex);
>  
>  	list_del(&rng->list);
> -	if (current_rng == rng)
> +	if (current_rng == rng) {
> +		drop_current_rng();
>  		enable_best_rng();
> +	}

A similar fix was already in the cryptodev tree and I thought was part of
a recent pull request.

Thanks,
Tom

>  
>  	if (list_empty(&rng_list)) {
>  		mutex_unlock(&rng_mutex);
> 

Re: [PATCH] hwrng: Explicitly drop current_rng when unregistering rng device

[Keith Packard]

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Tom Lendacky <thomas.lendacky@amd.com> writes:

> A similar fix was already in the cryptodev tree and I thought was part of
> a recent pull request.

Yup, just saw it on master. I've checked and it will do pretty much the
same thing as my patch, with the addition of clearing
cur_rng_set_by_user, which is necessary. Thanks for looking at my patch!

-- 
-keith

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