[PATCH v2 2/6] hw_random: move some code out mutex_lock for avoiding underlying deadlock

Amos Kong
Thu, 18 Sep 2014 12:37:43 -0000

In next patch, we use reference counting for each struct hwrng,
changing reference count also needs to take mutex_lock. Before
releasing the lock, if we try to stop a kthread that waits to
take the lock to reduce the referencing count, deadlock will
occur.

Signed-off-by: Amos Kong <akong at redhat.com>
---
 drivers/char/hw_random/core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index b1b6042..a0905c8 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -474,12 +474,12 @@ void hwrng_unregister(struct hwrng *rng)
 		}
 	}
 	if (list_empty(&rng_list)) {
+		mutex_unlock(&rng_mutex);
 		unregister_miscdev();
 		if (hwrng_fill)
 			kthread_stop(hwrng_fill);
-	}
-
-	mutex_unlock(&rng_mutex);
+	} else
+		mutex_unlock(&rng_mutex);
 }
 EXPORT_SYMBOL_GPL(hwrng_unregister);

--
1.9.3