On Sat, 2021-06-12 at 08:43 +0800, Ian Kent wrote:

On Sat, 2021-06-12 at 00:07 +0000, Al Viro wrote:

quoted

On Wed, Jun 09, 2021 at 04:50:27PM +0800, Ian Kent wrote:

quoted

+       if (d_really_is_negative(dentry)) {
+               struct dentry *d_parent = dget_parent(dentry);
+               struct kernfs_node *parent;

What the hell is dget_parent() for?  You don't do anything blocking
here, so why not simply grab dentry->d_lock - that'll stabilize
the value of ->d_parent just fine.  Just don't forget to drop the
lock before returning and that's it...

Thanks Al, I'll change it.

But if I change to take the read lock to ensure there's no operation
in progress for the revision check I would need the dget_parent(), yes?

quoted

quoted

+               /* If the kernfs parent node has changed discard
and
+                * proceed to ->lookup.
+                */
+               parent = kernfs_dentry_node(d_parent);
+               if (parent) {
+                       if (kernfs_dir_changed(parent, dentry)) {
+                               dput(d_parent);
+                               return 0;
+                       }
+               }
+               dput(d_parent);
+
+               /* The kernfs node doesn't exist, leave the
dentry
+                * negative and return success.
+                */
+               return 1;
+       }