ocfs2: avoid system inode ref confusion by adding mutex lock

The following case may lead to the same system inode ref in confusion.

A thread                            B thread
ocfs2_get_system_file_inode
->get_local_system_inode
->_ocfs2_get_system_file_inode
                                    because of *arr == NULL,
                                    ocfs2_get_system_file_inode
                                    ->get_local_system_inode
                                    ->_ocfs2_get_system_file_inode
gets first ref thru
_ocfs2_get_system_file_inode,
gets second ref thru igrab and
set *arr = inode
                                    at the moment, B thread also gets
                                    two refs, so lead to one more
                                    inode ref.

So add mutex lock to avoid multi thread set two inode ref once at the
same time.

Signed-off-by: jiangyiwen <jiangyiwen@huawei.com>
Reviewed-by: Joseph Qi <joseph.qi@huawei.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 7 insertions, 0 deletions

diff --git a/fs/ocfs2/ocfs2.h b/fs/ocfs2/ocfs2.h
index a780e20d4fba..8d64a97a9d5e 100644
--- a/fs/ocfs2/ocfs2.h
+++ b/fs/ocfs2/ocfs2.h
@@ -446,6 +446,8 @@ struct ocfs2_super
         /* rb tree root for refcount lock. */
         struct rb_root  osb_rf_lock_tree;
         struct ocfs2_refcount_tree *osb_ref_tree_lru;
+
+        struct mutex system_file_mutex;
 };
 
 #define OCFS2_SB(sb)        ((struct ocfs2_super *)(sb)->s_fs_info)
diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
index 888a1457af96..1aecd626e645 100644
--- a/fs/ocfs2/super.c
+++ b/fs/ocfs2/super.c
@@ -2100,6 +2100,8 @@ static int ocfs2_initialize_super(struct super_block *sb,
         spin_lock_init(&osb->osb_xattr_lock);
         ocfs2_init_steal_slots(osb);
 
+        mutex_init(&osb->system_file_mutex);
+
         atomic_set(&osb->alloc_stats.moves, 0);
         atomic_set(&osb->alloc_stats.local_data, 0);
         atomic_set(&osb->alloc_stats.bitmap_data, 0);
diff --git a/fs/ocfs2/sysfile.c b/fs/ocfs2/sysfile.c
index f053688d22a3..af155c183123 100644
--- a/fs/ocfs2/sysfile.c
+++ b/fs/ocfs2/sysfile.c
@@ -113,9 +113,11 @@ struct inode *ocfs2_get_system_file_inode(struct ocfs2_super *osb,
         } else
                 arr = get_local_system_inode(osb, type, slot);
 
+        mutex_lock(&osb->system_file_mutex);
         if (arr && ((inode = *arr) != NULL)) {
                 /* get a ref in addition to the array ref */
                 inode = igrab(inode);
+                mutex_unlock(&osb->system_file_mutex);
                 BUG_ON(!inode);
 
                 return inode;
@@ -129,6 +131,7 @@ struct inode *ocfs2_get_system_file_inode(struct ocfs2_super *osb,
                 *arr = igrab(inode);
                 BUG_ON(!*arr);
         }
+        mutex_unlock(&osb->system_file_mutex);
         return inode;
 }