hwrng: core - Fix current_rng init/cleanup race yet again

The kref solution is still buggy because we were only focusing
on the register/unregister race.  The same race affects the
setting of current_rng through sysfs.

This patch fixes it by using kref_get_unless_zero.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 11 insertions, 3 deletions

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 3dba2cf50241..42827fd5f38d 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -105,7 +105,6 @@ static inline void cleanup_rng(struct kref *kref)
 static void set_current_rng(struct hwrng *rng)
 {
         BUG_ON(!mutex_is_locked(&rng_mutex));
-        kref_get(&rng->ref);
         current_rng = rng;
 }
 
@@ -150,6 +149,9 @@ static void put_rng(struct hwrng *rng)
 
 static inline int hwrng_init(struct hwrng *rng)
 {
+        if (kref_get_unless_zero(&rng->ref))
+                goto skip_init;
+
         if (rng->init) {
                 int ret;
 
@@ -157,6 +159,11 @@ static inline int hwrng_init(struct hwrng *rng)
                 if (ret)
                         return ret;
         }
+
+        kref_init(&rng->ref);
+        reinit_completion(&rng->cleanup_done);
+
+skip_init:
         add_early_randomness(rng);
 
         current_quality = rng->quality ? : default_quality;
@@ -467,6 +474,9 @@ int hwrng_register(struct hwrng *rng)
                         goto out_unlock;
         }
 
+        init_completion(&rng->cleanup_done);
+        complete(&rng->cleanup_done);
+
         old_rng = current_rng;
         err = 0;
         if (!old_rng) {
@@ -494,8 +504,6 @@ int hwrng_register(struct hwrng *rng)
                 add_early_randomness(rng);
         }
 
-        init_completion(&rng->cleanup_done);
-
 out_unlock:
         mutex_unlock(&rng_mutex);
 out: