libfs: take cursors out of list when moving past the end of directory

that eliminates the last place where we accessed the tail of ->d_subdirs

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

diff --git a/fs/libfs.c b/fs/libfs.c
index 8e023b0..540611b 100644 (file)
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -92,14 +92,13 @@ EXPORT_SYMBOL(dcache_dir_close);
 /*
  * Returns an element of siblings' list.
  * We are looking for <count>th positive after <p>; if
- * found, dentry is grabbed and passed to caller via *<res>.
- * If no such element exists, the anchor of list is returned
- * and *<res> is set to NULL.
+ * found, dentry is grabbed and returned to caller.
+ * If no such element exists, NULL is returned.
  */
-static struct list_head *scan_positives(struct dentry *cursor,
+static struct dentry *scan_positives(struct dentry *cursor,
                                        struct list_head *p,
                                        loff_t count,
-                                       struct dentry **res)
+                                       struct dentry *last)
 {
        struct dentry *dentry = cursor->d_parent, *found = NULL;
 
@@ -127,9 +126,8 @@ static struct list_head *scan_positives(struct dentry *cursor,
                }
        }
        spin_unlock(&dentry->d_lock);
-       dput(*res);
-       *res = found;
-       return p;
+       dput(last);
+       return found;
 }
 
 loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence)
@@ -149,25 +147,22 @@ loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence)
        if (offset != file->f_pos) {
                struct dentry *cursor = file->private_data;
                struct dentry *to = NULL;
-               struct list_head *p;
 
-               file->f_pos = offset;
                inode_lock_shared(dentry->d_inode);
 
-               if (file->f_pos > 2) {
-                       p = scan_positives(cursor, &dentry->d_subdirs,
-                                          file->f_pos - 2, &to);
-                       spin_lock(&dentry->d_lock);
-                       list_move(&cursor->d_child, p);
-                       spin_unlock(&dentry->d_lock);
-               } else {
-                       spin_lock(&dentry->d_lock);
+               if (offset > 2)
+                       to = scan_positives(cursor, &dentry->d_subdirs,
+                                           offset - 2, NULL);
+               spin_lock(&dentry->d_lock);
+               if (to)
+                       list_move(&cursor->d_child, &to->d_child);
+               else
                        list_del_init(&cursor->d_child);
-                       spin_unlock(&dentry->d_lock);
-               }
-
+               spin_unlock(&dentry->d_lock);
                dput(to);
 
+               file->f_pos = offset;
+
                inode_unlock_shared(dentry->d_inode);
        }
        return offset;
@@ -199,17 +194,23 @@ int dcache_readdir(struct file *file, struct dir_context *ctx)
 
        if (ctx->pos == 2)
                p = anchor;
-       else
+       else if (!list_empty(&cursor->d_child))
                p = &cursor->d_child;
+       else
+               return 0;
 
-       while ((p = scan_positives(cursor, p, 1, &next)) != anchor) {
+       while ((next = scan_positives(cursor, p, 1, next)) != NULL) {
                if (!dir_emit(ctx, next->d_name.name, next->d_name.len,
                              d_inode(next)->i_ino, dt_type(d_inode(next))))
                        break;
                ctx->pos++;
+               p = &next->d_child;
        }
        spin_lock(&dentry->d_lock);
-       list_move_tail(&cursor->d_child, p);
+       if (next)
+               list_move_tail(&cursor->d_child, &next->d_child);
+       else
+               list_del_init(&cursor->d_child);
        spin_unlock(&dentry->d_lock);
        dput(next);