UBIFS: do not use inc_link when i_nlink is zero

This patch changes the 'i_nlink' counter handling in 'ubifs_unlink()',
'ubifs_rmdir()' and 'ubifs_rename()'. In these function  'i_nlink' may become 0,
and if 'ubifs_jnl_update()' failed, we would use 'inc_nlink()' to restore
the previous 'i_nlink' value, which is incorrect from the VFS point of view and
would cause a 'WARN_ON()' (see 'inc_nlink() implementation).

This patches saves the previous 'i_nlink' value in a local variable and uses it
at the error path instead of calling 'inc_nlink()'. We do this only for the
inodes where 'i_nlink' may potentially become zero.

This change has been requested by Al Viro <viro@ZenIV.linux.org.uk>.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

diff --git a/fs/ubifs/dir.c b/fs/ubifs/dir.c
index d6fe1c7..ec9f187 100644 (file)
--- a/fs/ubifs/dir.c
+++ b/fs/ubifs/dir.c
@@ -566,6 +566,7 @@ static int ubifs_unlink(struct inode *dir, struct dentry *dentry)
        int sz_change = CALC_DENT_SIZE(dentry->d_name.len);
        int err, budgeted = 1;
        struct ubifs_budget_req req = { .mod_dent = 1, .dirtied_ino = 2 };
+       unsigned int saved_nlink = inode->i_nlink;
 
        /*
         * Budget request settings: deletion direntry, deletion inode (+1 for
@@ -613,7 +614,7 @@ static int ubifs_unlink(struct inode *dir, struct dentry *dentry)
 out_cancel:
        dir->i_size += sz_change;
        dir_ui->ui_size = dir->i_size;
-       inc_nlink(inode);
+       set_nlink(inode, saved_nlink);
        unlock_2_inodes(dir, inode);
        if (budgeted)
                ubifs_release_budget(c, &req);
@@ -704,8 +705,7 @@ out_cancel:
        dir->i_size += sz_change;
        dir_ui->ui_size = dir->i_size;
        inc_nlink(dir);
-       inc_nlink(inode);
-       inc_nlink(inode);
+       set_nlink(inode, 2);
        unlock_2_inodes(dir, inode);
        if (budgeted)
                ubifs_release_budget(c, &req);
@@ -977,6 +977,7 @@ static int ubifs_rename(struct inode *old_dir, struct dentry *old_dentry,
        struct ubifs_budget_req ino_req = { .dirtied_ino = 1,
                        .dirtied_ino_d = ALIGN(old_inode_ui->data_len, 8) };
        struct timespec time;
+       unsigned int saved_nlink;
 
        /*
         * Budget request settings: deletion direntry, new direntry, removing
@@ -1059,13 +1060,14 @@ static int ubifs_rename(struct inode *old_dir, struct dentry *old_dentry,
        if (unlink) {
                /*
                 * Directories cannot have hard-links, so if this is a
-                * directory, decrement its @i_nlink twice because an empty
-                * directory has @i_nlink 2.
+                * directory, just clear @i_nlink.
                 */
+               saved_nlink = new_inode->i_nlink;
                if (is_dir)
+                       clear_nlink(new_inode);
+               else
                        drop_nlink(new_inode);
                new_inode->i_ctime = time;
-               drop_nlink(new_inode);
        } else {
                new_dir->i_size += new_sz;
                ubifs_inode(new_dir)->ui_size = new_dir->i_size;
@@ -1102,9 +1104,7 @@ static int ubifs_rename(struct inode *old_dir, struct dentry *old_dentry,
 
 out_cancel:
        if (unlink) {
-               if (is_dir)
-                       inc_nlink(new_inode);
-               inc_nlink(new_inode);
+               set_nlink(new_inode, saved_nlink);
        } else {
                new_dir->i_size -= new_sz;
                ubifs_inode(new_dir)->ui_size = new_dir->i_size;