[PATCH v2 4/6] hw_random: fix unregister race.

[Amos Kong <akong@redhat.com>]

From: Rusty Russell <rusty@rustcorp.com.au>

The previous patch added one potential problem: we can still be
reading from a hwrng when it's unregistered.  Add a wait for zero
in the hwrng_unregister path.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
 drivers/char/hw_random/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index ee9e504..9f6f5bb 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -60,6 +60,7 @@ static DEFINE_MUTEX(rng_mutex);
 static DEFINE_MUTEX(reading_mutex);
 static int data_avail;
 static u8 *rng_buffer, *rng_fillbuf;
+static DECLARE_WAIT_QUEUE_HEAD(rng_done);
 static unsigned short current_quality;
 static unsigned short default_quality; /* = 0; default to "off" */
 
@@ -98,6 +99,7 @@ static inline void cleanup_rng(struct kref *kref)
 
 	if (rng->cleanup)
 		rng->cleanup(rng);
+	wake_up_all(&rng_done);
 }
 
 static void set_current_rng(struct hwrng *rng)
-- 
1.9.3