debugfs: leave freeing a symlink body until inode eviction

As it is, we have debugfs_remove() racing with symlink traversals.
Supply ->evict_inode() and do freeing there - inode will remain
pinned until we are done with the symlink body.

And rip the idiocy with checking if dentry is positive right after
we'd verified debugfs_positive(), which is a stronger check...

Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index 9093364..96400ab 100644 (file)
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -169,10 +169,19 @@ static int debugfs_show_options(struct seq_file *m, struct dentry *root)
        return 0;
 }
 
+static void debugfs_evict_inode(struct inode *inode)
+{
+       truncate_inode_pages_final(&inode->i_data);
+       clear_inode(inode);
+       if (S_ISLNK(inode->i_mode))
+               kfree(inode->i_private);
+}
+
 static const struct super_operations debugfs_super_operations = {
        .statfs         = simple_statfs,
        .remount_fs     = debugfs_remount,
        .show_options   = debugfs_show_options,
+       .evict_inode    = debugfs_evict_inode,
 };
 
 static struct vfsmount *debugfs_automount(struct path *path)
@@ -511,23 +520,14 @@ static int __debugfs_remove(struct dentry *dentry, struct dentry *parent)
        int ret = 0;
 
        if (debugfs_positive(dentry)) {
-               if (dentry->d_inode) {
-                       dget(dentry);
-                       switch (dentry->d_inode->i_mode & S_IFMT) {
-                       case S_IFDIR:
-                               ret = simple_rmdir(parent->d_inode, dentry);
-                               break;
-                       case S_IFLNK:
-                               kfree(dentry->d_inode->i_private);
-                               /* fall through */
-                       default:
-                               simple_unlink(parent->d_inode, dentry);
-                               break;
-                       }
-                       if (!ret)
-                               d_delete(dentry);
-                       dput(dentry);
-               }
+               dget(dentry);
+               if (S_ISDIR(dentry->d_inode->i_mode))
+                       ret = simple_rmdir(parent->d_inode, dentry);
+               else
+                       simple_unlink(parent->d_inode, dentry);
+               if (!ret)
+                       d_delete(dentry);
+               dput(dentry);
        }
        return ret;
 }