Revert "kernfs: Change kernfs_notify_list to llist."

This reverts commit aab43507e4d8047b0de2d7b1376ec15a733502a5.

This is causing regression due to same kernfs_node getting
added multiple times in kernfs_notify_list so revert it until
safe way of using llist in this context is found.

Reported-by: Nathan Chancellor <nathan@kernel.org>
Reported-by: Michael Walle <michael@walle.cc>
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
Cc: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20220705201026.2487665-1-imran.f.khan@oracle.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index bb933221b4bae1f8c242cb05e0494993682095d8..baff4b1d40c760df49f4a26d2044d451e818ea65 100644 (file)
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -25,16 +25,18 @@ struct kernfs_open_node {
        struct list_head        files; /* goes through kernfs_open_file.list */
 };
 
-/**
- * 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)
+/*
+ * 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.
  */
-#define attribute_to_node(ptr, type, member)   \
-       container_of(ptr, type, member)
+#define KERNFS_NOTIFY_EOL                      ((void *)&kernfs_notify_list)
 
-static LLIST_HEAD(kernfs_notify_list);
+static DEFINE_SPINLOCK(kernfs_notify_lock);
+static struct kernfs_node *kernfs_notify_list = KERNFS_NOTIFY_EOL;
 
 static inline struct mutex *kernfs_open_file_mutex_ptr(struct kernfs_node *kn)
 {
@@ -909,16 +911,18 @@ 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 */
-       free = llist_del_first(&kernfs_notify_list);
-       if (free == NULL)
+       spin_lock_irq(&kernfs_notify_lock);
+       kn = kernfs_notify_list;
+       if (kn == KERNFS_NOTIFY_EOL) {
+               spin_unlock_irq(&kernfs_notify_lock);
                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);
@@ -974,14 +978,12 @@ repeat:
 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);
@@ -992,9 +994,14 @@ void kernfs_notify(struct kernfs_node *kn)
        rcu_read_unlock();
 
        /* schedule work to kick fsnotify */
-       kernfs_get(kn);
-       llist_add(&kn->attr.notify_next, &kernfs_notify_list);
-       schedule_work(&kernfs_notify_work);
+       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);
 }
 EXPORT_SYMBOL_GPL(kernfs_notify);
 

diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 13e703f615f7921fa4d4c0409f3faf7a01aaaa61..367044d7708c6f32357d82853b48f87499bd7cd1 100644 (file)
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -173,7 +173,7 @@ struct kernfs_elem_attr {
        const struct kernfs_ops *ops;
        struct kernfs_open_node __rcu   *open;
        loff_t                  size;
-       struct llist_node       notify_next;    /* for kernfs_notify() */
+       struct kernfs_node      *notify_next;   /* for kernfs_notify() */
 };
 
 /*