d_make_discardable(): warn if given a non-persistent dentry

At this point there are very few call chains that might lead to
d_make_discardable() on a dentry that hadn't been made persistent:
calls of simple_unlink() and simple_rmdir() in configfs and
apparmorfs.

Both filesystems do pin (part of) their contents in dcache, but
they are currently playing very unusual games with that.  Converting
them to more usual patterns might be possible, but it's definitely
going to be a long series of changes in both cases.

For now the easiest solution is to have both stop using simple_unlink()
and simple_rmdir() - that allows to make d_make_discardable() warn
when given a non-persistent dentry.

Rather than giving them full-blown private copies (with calls of
d_make_discardable() replaced with dput()), let's pull the parts of
simple_unlink() and simple_rmdir() that deal with timestamps and link
counts into separate helpers (__simple_unlink() and __simple_rmdir()
resp.) and have those used by configfs and apparmorfs.

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

fs/configfs/dir.c

@@ -400,8 +400,14 @@ static void remove_dir(struct dentry * d)
 
 	configfs_remove_dirent(d);
 
-	if (d_really_is_positive(d))
-		simple_rmdir(d_inode(parent),d);
+	if (d_really_is_positive(d)) {
+		if (likely(simple_empty(d))) {
+			__simple_rmdir(d_inode(parent),d);
+			dput(d);
+		} else {
+			pr_warn("remove_dir (%pd): attributes remain", d);
+		}
+	}
 
 	pr_debug(" o %pd removing done (%d)\n", d, d_count(d));
 

fs/configfs/inode.c

@@ -211,7 +211,8 @@ void configfs_drop_dentry(struct configfs_dirent * sd, struct dentry * parent)
 			dget_dlock(dentry);
 			__d_drop(dentry);
 			spin_unlock(&dentry->d_lock);
-			simple_unlink(d_inode(parent), dentry);
+			__simple_unlink(d_inode(parent), dentry);
+			dput(dentry);
 		} else
 			spin_unlock(&dentry->d_lock);
 	}

fs/dcache.c

@@ -931,14 +931,7 @@ EXPORT_SYMBOL(dput);
 void d_make_discardable(struct dentry *dentry)
 {
 	spin_lock(&dentry->d_lock);
-	/*
-	 * By the end of the series we'll add
-	 * WARN_ON(!(dentry->d_flags & DCACHE_PERSISTENT);
-	 * here, but while object removal is done by a few common helpers,
-	 * object creation tends to be open-coded (if nothing else, new inode
-	 * needs to be set up), so adding a warning from the very beginning
-	 * would make for much messier patch series.
-	 */
+	WARN_ON(!(dentry->d_flags & DCACHE_PERSISTENT));
 	dentry->d_flags &= ~DCACHE_PERSISTENT;
 	dentry->d_lockref.count--;
 	rcu_read_lock();

fs/libfs.c

@@ -790,13 +790,27 @@ int simple_empty(struct dentry *dentry)
 }
 EXPORT_SYMBOL(simple_empty);
 
-int simple_unlink(struct inode *dir, struct dentry *dentry)
+void __simple_unlink(struct inode *dir, struct dentry *dentry)
 {
 	struct inode *inode = d_inode(dentry);
 
 	inode_set_mtime_to_ts(dir,
 			      inode_set_ctime_to_ts(dir, inode_set_ctime_current(inode)));
 	drop_nlink(inode);
+}
+EXPORT_SYMBOL(__simple_unlink);
+
+void __simple_rmdir(struct inode *dir, struct dentry *dentry)
+{
+	drop_nlink(d_inode(dentry));
+	__simple_unlink(dir, dentry);
+	drop_nlink(dir);
+}
+EXPORT_SYMBOL(__simple_rmdir);
+
+int simple_unlink(struct inode *dir, struct dentry *dentry)
+{
+	__simple_unlink(dir, dentry);
 	d_make_discardable(dentry);
 	return 0;
 }
@@ -807,9 +821,8 @@ int simple_rmdir(struct inode *dir, struct dentry *dentry)
 	if (!simple_empty(dentry))
 		return -ENOTEMPTY;
 
-	drop_nlink(d_inode(dentry));
-	simple_unlink(dir, dentry);
-	drop_nlink(dir);
+	__simple_rmdir(dir, dentry);
+	d_make_discardable(dentry);
 	return 0;
 }
 EXPORT_SYMBOL(simple_rmdir);

include/linux/fs.h

@@ -3621,6 +3621,8 @@ extern int simple_open(struct inode *inode, struct file *file);
 extern int simple_link(struct dentry *, struct inode *, struct dentry *);
 extern int simple_unlink(struct inode *, struct dentry *);
 extern int simple_rmdir(struct inode *, struct dentry *);
+extern void __simple_unlink(struct inode *, struct dentry *);
+extern void __simple_rmdir(struct inode *, struct dentry *);
 void simple_rename_timestamp(struct inode *old_dir, struct dentry *old_dentry,
 			     struct inode *new_dir, struct dentry *new_dentry);
 extern int simple_rename_exchange(struct inode *old_dir, struct dentry *old_dentry,

security/apparmor/apparmorfs.c

@@ -358,10 +358,15 @@ static void aafs_remove(struct dentry *dentry)
 	dir = d_inode(dentry->d_parent);
 	inode_lock(dir);
 	if (simple_positive(dentry)) {
-		if (d_is_dir(dentry))
-			simple_rmdir(dir, dentry);
-		else
-			simple_unlink(dir, dentry);
+		if (d_is_dir(dentry)) {
+			if (!WARN_ON(!simple_empty(dentry))) {
+				__simple_rmdir(dir, dentry);
+				dput(dentry);
+			}
+		} else {
+			__simple_unlink(dir, dentry);
+			dput(dentry);
+		}
 		d_delete(dentry);
 		dput(dentry);
 	}