kernfs: Backport kernfs locking fix patchset

fs/kernfs/dir.c

@@ -27,7 +27,7 @@ static DEFINE_RWLOCK(kernfs_rename_lock);	/* kn->parent and ->name */
  */
 static DEFINE_SPINLOCK(kernfs_pr_cont_lock);
 static char kernfs_pr_cont_buf[PATH_MAX];	/* protected by pr_cont_lock */
-static DEFINE_RAW_SPINLOCK(kernfs_idr_lock);	/* root->ino_idr */
+static DEFINE_SPINLOCK(kernfs_idr_lock);	/* root->ino_idr */
 
 #define rb_to_kn(X) rb_entry((X), struct kernfs_node, rb)
 
@@ -529,6 +529,20 @@ void kernfs_get(struct kernfs_node *kn)
 }
 EXPORT_SYMBOL_GPL(kernfs_get);
 
+static void kernfs_free_rcu(struct rcu_head *rcu)
+{
+	struct kernfs_node *kn = container_of(rcu, struct kernfs_node, rcu);
+
+	kfree_const(kn->name);
+
+	if (kn->iattr) {
+		simple_xattrs_free(&kn->iattr->xattrs, NULL);
+		kmem_cache_free(kernfs_iattrs_cache, kn->iattr);
+	}
+
+	kmem_cache_free(kernfs_node_cache, kn);
+}
+
 /**
  * kernfs_put - put a reference count on a kernfs_node
  * @kn: the target kernfs_node
@@ -539,7 +553,6 @@ void kernfs_put(struct kernfs_node *kn)
 {
 	struct kernfs_node *parent;
 	struct kernfs_root *root;
-	unsigned long flags;
 
 	if (!kn || !atomic_dec_and_test(&kn->count))
 		return;
@@ -558,16 +571,11 @@ void kernfs_put(struct kernfs_node *kn)
 	if (kernfs_type(kn) == KERNFS_LINK)
 		kernfs_put(kn->symlink.target_kn);
 
-	kfree_const(kn->name);
-
-	if (kn->iattr) {
-		simple_xattrs_free(&kn->iattr->xattrs, NULL);
-		kmem_cache_free(kernfs_iattrs_cache, kn->iattr);
-	}
-	raw_spin_lock_irqsave(&kernfs_idr_lock, flags);
+	spin_lock(&kernfs_idr_lock);
 	idr_remove(&root->ino_idr, (u32)kernfs_ino(kn));
-	raw_spin_unlock_irqrestore(&kernfs_idr_lock, flags);
-	kmem_cache_free(kernfs_node_cache, kn);
+	spin_unlock(&kernfs_idr_lock);
+
+	call_rcu(&kn->rcu, kernfs_free_rcu);
 
 	kn = parent;
 	if (kn) {
@@ -576,7 +584,7 @@ void kernfs_put(struct kernfs_node *kn)
 	} else {
 		/* just released the root kn, free @root too */
 		idr_destroy(&root->ino_idr);
-		kfree(root);
+		kfree_rcu(root, rcu);
 	}
 }
 EXPORT_SYMBOL_GPL(kernfs_put);
@@ -608,7 +616,6 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
 	struct kernfs_node *kn;
 	u32 id_highbits;
 	int ret;
-	unsigned long irqflags;
 
 	name = kstrdup_const(name, GFP_KERNEL);
 	if (!name)
@@ -619,13 +626,13 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
 		goto err_out1;
 
 	idr_preload(GFP_KERNEL);
-	raw_spin_lock_irqsave(&kernfs_idr_lock, irqflags);
+	spin_lock(&kernfs_idr_lock);
 	ret = idr_alloc_cyclic(&root->ino_idr, kn, 1, 0, GFP_ATOMIC);
 	if (ret >= 0 && ret < root->last_id_lowbits)
 		root->id_highbits++;
 	id_highbits = root->id_highbits;
 	root->last_id_lowbits = ret;
-	raw_spin_unlock_irqrestore(&kernfs_idr_lock, irqflags);
+	spin_unlock(&kernfs_idr_lock);
 	idr_preload_end();
 	if (ret < 0)
 		goto err_out2;
@@ -661,9 +668,9 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
 	return kn;
 
  err_out3:
-	raw_spin_lock_irqsave(&kernfs_idr_lock, irqflags);
+	spin_lock(&kernfs_idr_lock);
 	idr_remove(&root->ino_idr, (u32)kernfs_ino(kn));
-	raw_spin_unlock_irqrestore(&kernfs_idr_lock, irqflags);
+	spin_unlock(&kernfs_idr_lock);
  err_out2:
 	kmem_cache_free(kernfs_node_cache, kn);
  err_out1:
@@ -704,9 +711,8 @@ struct kernfs_node *kernfs_find_and_get_node_by_id(struct kernfs_root *root,
 	struct kernfs_node *kn;
 	ino_t ino = kernfs_id_ino(id);
 	u32 gen = kernfs_id_gen(id);
-	unsigned long flags;
 
-	raw_spin_lock_irqsave(&kernfs_idr_lock, flags);
+	rcu_read_lock();
 
 	kn = idr_find(&root->ino_idr, (u32)ino);
 	if (!kn)
@@ -730,10 +736,10 @@ struct kernfs_node *kernfs_find_and_get_node_by_id(struct kernfs_root *root,
 	if (unlikely(!__kernfs_active(kn) || !atomic_inc_not_zero(&kn->count)))
 		goto err_unlock;
 
-	raw_spin_unlock_irqrestore(&kernfs_idr_lock, flags);
+	rcu_read_unlock();
 	return kn;
 err_unlock:
-	raw_spin_unlock_irqrestore(&kernfs_idr_lock, flags);
+	rcu_read_unlock();
 	return NULL;
 }
 

fs/kernfs/kernfs-internal.h

@@ -49,6 +49,8 @@ struct kernfs_root {
 	struct rw_semaphore	kernfs_rwsem;
 	struct rw_semaphore	kernfs_iattr_rwsem;
 	struct rw_semaphore	kernfs_supers_rwsem;
+
+	struct rcu_head		rcu;
 };
 
 /* +1 to avoid triggering overflow warning when negating it */

include/linux/kernfs.h

@@ -206,6 +206,9 @@ struct kernfs_node {
 
 	const void		*ns;	/* namespace tag */
 	unsigned int		hash;	/* ns + name hash */
+	unsigned short		flags;
+	umode_t			mode;
+
 	union {
 		struct kernfs_elem_dir		dir;
 		struct kernfs_elem_symlink	symlink;
@@ -220,9 +223,9 @@ struct kernfs_node {
 	 */
 	u64			id;
 
-	unsigned short		flags;
-	umode_t			mode;
 	struct kernfs_iattrs	*iattr;
+
+	struct rcu_head		rcu;
 };
 
 /*