1 files changed, 19 insertions, 17 deletions

diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index f587aded46b5..9dca4da059b3 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -184,7 +184,10 @@ static const struct super_operations debugfs_super_operations = {
 
 static void debugfs_release_dentry(struct dentry *dentry)
 {
-	kfree(dentry->d_fsdata);
+	void *fsd = dentry->d_fsdata;
+
+	if (!((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT))
+		kfree(dentry->d_fsdata);
 }
 
 static struct vfsmount *debugfs_automount(struct path *path)
@@ -344,35 +347,25 @@ static struct dentry *__debugfs_create_file(const char *name, umode_t mode,
 {
 	struct dentry *dentry;
 	struct inode *inode;
-	struct debugfs_fsdata *fsd;
-
-	fsd = kmalloc(sizeof(*fsd), GFP_KERNEL);
-	if (!fsd)
-		return NULL;
 
 	if (!(mode & S_IFMT))
 		mode |= S_IFREG;
 	BUG_ON(!S_ISREG(mode));
 	dentry = start_creating(name, parent);
 
-	if (IS_ERR(dentry)) {
-		kfree(fsd);
+	if (IS_ERR(dentry))
 		return NULL;
-	}
 
 	inode = debugfs_get_inode(dentry->d_sb);
-	if (unlikely(!inode)) {
-		kfree(fsd);
+	if (unlikely(!inode))
 		return failed_creating(dentry);
-	}
 
 	inode->i_mode = mode;
 	inode->i_private = data;
 
 	inode->i_fop = proxy_fops;
-	fsd->real_fops = real_fops;
-	refcount_set(&fsd->active_users, 1);
-	dentry->d_fsdata = fsd;
+	dentry->d_fsdata = (void *)((unsigned long)real_fops |
+				DEBUGFS_FSDATA_IS_REAL_FOPS_BIT);
 
 	d_instantiate(dentry, inode);
 	fsnotify_create(d_inode(dentry->d_parent), dentry);
@@ -635,8 +628,17 @@ static void __debugfs_remove_file(struct dentry *dentry, struct dentry *parent)
 
 	simple_unlink(d_inode(parent), dentry);
 	d_delete(dentry);
-	fsd = dentry->d_fsdata;
-	init_completion(&fsd->active_users_drained);
+
+	/*
+	 * Paired with the closing smp_mb() implied by a successful
+	 * cmpxchg() in debugfs_file_get(): either
+	 * debugfs_file_get() must see a dead dentry or we must see a
+	 * debugfs_fsdata instance at ->d_fsdata here (or both).
+	 */
+	smp_mb();
+	fsd = READ_ONCE(dentry->d_fsdata);
+	if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)
+		return;
 	if (!refcount_dec_and_test(&fsd->active_users))
 		wait_for_completion(&fsd->active_users_drained);
 }