At present kernfs_notify_list is implemented as a singly linked
list of kernfs_node(s), where last element points to itself and
value of ->attr.next tells if node is present on the list or not.
Both addition and deletion to list happen under kernfs_notify_lock.
Change kernfs_notify_list to llist so that addition to list can heppen
locklessly. We still need kernfs_notify_lock for consumers (kernfs_notify\
_workfn) because there can be multiple concurrent work items.
Suggested by: Al Viro <[email protected]>
Signed-off-by: Imran Khan <[email protected]>
Acked-by: Tejun Heo <[email protected]>
---
fs/kernfs/file.c | 47 ++++++++++++++++++------------------------
include/linux/kernfs.h | 2 +-
2 files changed, 21 insertions(+), 28 deletions(-)
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 8264e28f9098..3f883601c5ec 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -38,18 +38,16 @@ struct kernfs_open_node {
struct list_head files; /* goes through kernfs_open_file.list */
};
-/*
- * kernfs_notify() may be called from any context and bounces notifications
- * through a work item. To minimize space overhead in kernfs_node, the
- * pending queue is implemented as a singly linked list of kernfs_nodes.
- * The list is terminated with the self pointer so that whether a
- * kernfs_node is on the list or not can be determined by testing the next
- * pointer for NULL.
+/**
+ * attribute_to_node - get kernfs_node object corresponding to a kernfs attribute
+ * @ptr: &struct kernfs_elem_attr
+ * @type: struct kernfs_node
+ * @member: name of member (i.e attr)
*/
-#define KERNFS_NOTIFY_EOL ((void *)&kernfs_notify_list)
+#define attribute_to_node(ptr, type, member) \
+ container_of(ptr, type, member)
-static DEFINE_SPINLOCK(kernfs_notify_lock);
-static struct kernfs_node *kernfs_notify_list = KERNFS_NOTIFY_EOL;
+static LLIST_HEAD(kernfs_notify_list);
/**
* kernfs_deref_open_node - Get kernfs_open_node corresponding to @kn.
@@ -928,18 +926,16 @@ static void kernfs_notify_workfn(struct work_struct *work)
struct kernfs_node *kn;
struct kernfs_super_info *info;
struct kernfs_root *root;
+ struct llist_node *free;
+ struct kernfs_elem_attr *attr;
repeat:
/* pop one off the notify_list */
- spin_lock_irq(&kernfs_notify_lock);
- kn = kernfs_notify_list;
- if (kn == KERNFS_NOTIFY_EOL) {
- spin_unlock_irq(&kernfs_notify_lock);
+ free = llist_del_first(&kernfs_notify_list);
+ if (free == NULL)
return;
- }
- kernfs_notify_list = kn->attr.notify_next;
- kn->attr.notify_next = NULL;
- spin_unlock_irq(&kernfs_notify_lock);
+ attr = llist_entry(free, struct kernfs_elem_attr, notify_next);
+ kn = attribute_to_node(attr, struct kernfs_node, attr);
root = kernfs_root(kn);
/* kick fsnotify */
down_write(&root->kernfs_rwsem);
@@ -995,12 +991,14 @@ static void kernfs_notify_workfn(struct work_struct *work)
void kernfs_notify(struct kernfs_node *kn)
{
static DECLARE_WORK(kernfs_notify_work, kernfs_notify_workfn);
- unsigned long flags;
struct kernfs_open_node *on;
if (WARN_ON(kernfs_type(kn) != KERNFS_FILE))
return;
+ /* Because we are using llist for kernfs_notify_list */
+ WARN_ON_ONCE(in_nmi());
+
/* kick poll immediately */
rcu_read_lock();
on = rcu_dereference(kn->attr.open);
@@ -1011,14 +1009,9 @@ void kernfs_notify(struct kernfs_node *kn)
rcu_read_unlock();
/* schedule work to kick fsnotify */
- spin_lock_irqsave(&kernfs_notify_lock, flags);
- if (!kn->attr.notify_next) {
- kernfs_get(kn);
- kn->attr.notify_next = kernfs_notify_list;
- kernfs_notify_list = kn;
- schedule_work(&kernfs_notify_work);
- }
- spin_unlock_irqrestore(&kernfs_notify_lock, flags);
+ kernfs_get(kn);
+ llist_add(&kn->attr.notify_next, &kernfs_notify_list);
+ schedule_work(&kernfs_notify_work);
}
EXPORT_SYMBOL_GPL(kernfs_notify);
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 13f54f078a52..2dd9c8df0f4f 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -116,7 +116,7 @@ struct kernfs_elem_attr {
const struct kernfs_ops *ops;
struct kernfs_open_node __rcu *open;
loff_t size;
- struct kernfs_node *notify_next; /* for kernfs_notify() */
+ struct llist_node notify_next; /* for kernfs_notify() */
};
/*
--
2.30.2