ima: remove unnecessary i_mutex locking from ima_rdwr_violation_check()

Before 2.6.39 inode->i_readcount was maintained by IMA. It was not atomic
and protected using spinlock. For 2.6.39, i_readcount was converted to
atomic and maintaining was moved VFS layer. Spinlock for some unclear
reason was replaced by i_mutex.

After analyzing the code, we came to conclusion that i_mutex locking is
unnecessary, especially when an IMA policy has not been defined.

This patch removes i_mutex locking from ima_rdwr_violation_check().
Signed-off-by: Dmitry Kasatkin <d.kasatkin@samsung.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

security/integrity/ima/ima_main.c

@@ -88,8 +88,6 @@ static void ima_rdwr_violation_check(struct file *file)
 	if (!S_ISREG(inode->i_mode) || !ima_initialized)
 		return;
 
-	mutex_lock(&inode->i_mutex);	/* file metadata: permissions, xattr */
-
 	if (mode & FMODE_WRITE) {
 		if (atomic_read(&inode->i_readcount) && IS_IMA(inode)) {
 			struct integrity_iint_cache *iint;
@@ -104,8 +102,6 @@ static void ima_rdwr_violation_check(struct file *file)
 			send_writers = true;
 	}
 
-	mutex_unlock(&inode->i_mutex);
-
 	if (!send_tomtou && !send_writers)
 		return;