UBIFS: remove mst_mutex

The 'mst_mutex' is not needed since because 'ubifs_write_master()' is only
called on the mount path and commit path. The mount path is sequential and
there is no parallelism, and the commit path is also serialized - there is only
one commit going on at a time.
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

fs/ubifs/commit.c

@@ -174,7 +174,6 @@ static int do_commit(struct ubifs_info *c)
 	if (err)
 		goto out;
 
-	mutex_lock(&c->mst_mutex);
 	c->mst_node->cmt_no      = cpu_to_le64(c->cmt_no);
 	c->mst_node->log_lnum    = cpu_to_le32(new_ltail_lnum);
 	c->mst_node->root_lnum   = cpu_to_le32(zroot.lnum);
@@ -204,7 +203,6 @@ static int do_commit(struct ubifs_info *c)
 	else
 		c->mst_node->flags &= ~cpu_to_le32(UBIFS_MST_NO_ORPHS);
 	err = ubifs_write_master(c);
-	mutex_unlock(&c->mst_mutex);
 	if (err)
 		goto out;
 

fs/ubifs/master.c

@@ -352,10 +352,9 @@ int ubifs_read_master(struct ubifs_info *c)
  * ubifs_write_master - write master node.
  * @c: UBIFS file-system description object
  *
- * This function writes the master node. The caller has to take the
- * @c->mst_mutex lock before calling this function. Returns zero in case of
- * success and a negative error code in case of failure. The master node is
- * written twice to enable recovery.
+ * This function writes the master node. Returns zero in case of success and a
+ * negative error code in case of failure. The master node is written twice to
+ * enable recovery.
  */
 int ubifs_write_master(struct ubifs_info *c)
 {

fs/ubifs/super.c

@@ -1963,7 +1963,6 @@ static struct ubifs_info *alloc_ubifs_info(struct ubi_volume_desc *ubi)
 		mutex_init(&c->lp_mutex);
 		mutex_init(&c->tnc_mutex);
 		mutex_init(&c->log_mutex);
-		mutex_init(&c->mst_mutex);
 		mutex_init(&c->umount_mutex);
 		mutex_init(&c->bu_mutex);
 		mutex_init(&c->write_reserve_mutex);

fs/ubifs/ubifs.h

@@ -1049,7 +1049,6 @@ struct ubifs_debug_info;
  *
  * @mst_node: master node
  * @mst_offs: offset of valid master node
- * @mst_mutex: protects the master node area, @mst_node, and @mst_offs
  *
  * @max_bu_buf_len: maximum bulk-read buffer length
  * @bu_mutex: protects the pre-allocated bulk-read buffer and @c->bu
@@ -1290,7 +1289,6 @@ struct ubifs_info {
 
 	struct ubifs_mst_node *mst_node;
 	int mst_offs;
-	struct mutex mst_mutex;
 
 	int max_bu_buf_len;
 	struct mutex bu_mutex;