ceph: drop negative child dentries before try pruning inode's alias

BugLink: http://bugs.launchpad.net/bugs/1745052

commit 040d7860 upstream.

Negative child dentry holds reference on inode's alias, it makes
d_prune_aliases() do nothing.
Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

fs/ceph/mds_client.c

@@ -1400,6 +1400,29 @@ static int __close_session(struct ceph_mds_client *mdsc,
 	return request_close_session(mdsc, session);
 }
 
+static bool drop_negative_children(struct dentry *dentry)
+{
+	struct dentry *child;
+	bool all_negative = true;
+
+	if (!d_is_dir(dentry))
+		goto out;
+
+	spin_lock(&dentry->d_lock);
+	list_for_each_entry(child, &dentry->d_subdirs, d_child) {
+		if (d_really_is_positive(child)) {
+			all_negative = false;
+			break;
+		}
+	}
+	spin_unlock(&dentry->d_lock);
+
+	if (all_negative)
+		shrink_dcache_parent(dentry);
+out:
+	return all_negative;
+}
+
 /*
  * Trim old(er) caps.
  *
@@ -1445,16 +1468,27 @@ static int trim_caps_cb(struct inode *inode, struct ceph_cap *cap, void *arg)
 	if ((used | wanted) & ~oissued & mine)
 		goto out;   /* we need these caps */
 
-	session->s_trim_caps--;
 	if (oissued) {
 		/* we aren't the only cap.. just remove us */
 		__ceph_remove_cap(cap, true);
+		session->s_trim_caps--;
 	} else {
+		struct dentry *dentry;
 		/* try dropping referring dentries */
 		spin_unlock(&ci->i_ceph_lock);
-		d_prune_aliases(inode);
-		dout("trim_caps_cb %p cap %p  pruned, count now %d\n",
-		     inode, cap, atomic_read(&inode->i_count));
+		dentry = d_find_any_alias(inode);
+		if (dentry && drop_negative_children(dentry)) {
+			int count;
+			dput(dentry);
+			d_prune_aliases(inode);
+			count = atomic_read(&inode->i_count);
+			if (count == 1)
+				session->s_trim_caps--;
+			dout("trim_caps_cb %p cap %p pruned, count now %d\n",
+			     inode, cap, count);
+		} else {
+			dput(dentry);
+		}
 		return 0;
 	}