[PATCH] [keys] Use mutex instead of rw_semaphore for __key_link()serialisation

[Arun Raghavan]

__key_link() uses an rw_semaphore as a mutex to serialise link/link calls. 
This patch converts it to explicitly use a struct mutex.

Signed-off-by: Arun Raghavan <arunsr@xxxxxxxxxxxxxx>
Signed-off-by: Satyam Sharma <satyam@xxxxxxxxxxxxx>

---

 security/keys/keyring.c |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 5f31eb7..7bfc725 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -15,6 +15,7 @@
 #include <linux/slab.h>
 #include <linux/security.h>
 #include <linux/seq_file.h>
+#include <linux/mutex.h>
 #include <linux/err.h>
 #include <asm/uaccess.h>
 #include "internal.h"
@@ -69,10 +70,10 @@ struct key_type key_type_keyring = {
 EXPORT_SYMBOL(key_type_keyring);
 
 /*
- * semaphore to serialise link/link calls to prevent two link calls in parallel
+ * mutex to serialise link/link calls to prevent two link calls in parallel
  * introducing a cycle
  */
-static DECLARE_RWSEM(keyring_serialise_link_sem);
+static DEFINE_MUTEX(keyring_serialise_link_mutex);
 
 /*****************************************************************************/
 /*
@@ -681,7 +682,7 @@ int __key_link(struct key *keyring, struct key *key)
 
 	/* serialise link/link calls to prevent parallel calls causing a
 	 * cycle when applied to two keyring in opposite orders */
-	down_write(&keyring_serialise_link_sem);
+	mutex_lock(&keyring_serialise_link_mutex);
 
 	/* check that we aren't going to create a cycle adding one keyring to
 	 * another */
@@ -789,7 +790,7 @@ int __key_link(struct key *keyring, struct key *key)
 done:
 	ret = 0;
 error2:
-	up_write(&keyring_serialise_link_sem);
+	mutex_unlock(&keyring_serialise_link_mutex);
 error:
 	return ret;
 
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