[PATCH AUTOSEL for 4.15 77/78] hwrng: core - Clean up RNG list when last hwrng is unregistered

[Sasha Levin]

From: Gary R Hook <gary.hook@xxxxxxx>

[ Upstream commit 0e4b52942b1c76f89e0dcb829f72e123d0678f54 ]

Commit 142a27f0a731 added support for a "best" RNG, and in doing so
introduced a hang from rmmod/modprobe -r when the last RNG on the list
was unloaded.

When the hwrng list is depleted, return the global variables to their
original state and decrement all references to the object.

Fixes: 142a27f0a731 ("hwrng: core - Reset user selected rng by writing "" to rng_current")
Signed-off-by: Gary R Hook <gary.hook@xxxxxxx>
Reviewed-by: PrasannaKumar Muralidharan <prasannatsmkumar@xxxxxxxxx>
Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 drivers/char/hw_random/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 657b8770b6b9..91bb98c42a1c 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -306,6 +306,10 @@ static int enable_best_rng(void)
 		ret = ((new_rng == current_rng) ? 0 : set_current_rng(new_rng));
 		if (!ret)
 			cur_rng_set_by_user = 0;
+	} else {
+		drop_current_rng();
+		cur_rng_set_by_user = 0;
+		ret = 0;
 	}
 
 	return ret;
-- 
2.14.1