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-rw-r--r--fs/kernfs/dir.c57
1 files changed, 57 insertions, 0 deletions
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 33f711f6b86e..7be37c838007 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -508,6 +508,10 @@ void kernfs_put(struct kernfs_node *kn)
struct kernfs_node *parent;
struct kernfs_root *root;
+ /*
+ * kernfs_node is freed with ->count 0, kernfs_find_and_get_node_by_ino
+ * depends on this to filter reused stale node
+ */
if (!kn || !atomic_dec_and_test(&kn->count))
return;
root = kernfs_root(kn);
@@ -649,6 +653,11 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
kn->ino = ret;
kn->generation = gen;
+ /*
+ * set ino first. This barrier is paired with atomic_inc_not_zero in
+ * kernfs_find_and_get_node_by_ino
+ */
+ smp_mb__before_atomic();
atomic_set(&kn->count, 1);
atomic_set(&kn->active, KN_DEACTIVATED_BIAS);
RB_CLEAR_NODE(&kn->rb);
@@ -680,6 +689,54 @@ struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
return kn;
}
+/*
+ * kernfs_find_and_get_node_by_ino - get kernfs_node from inode number
+ * @root: the kernfs root
+ * @ino: inode number
+ *
+ * RETURNS:
+ * NULL on failure. Return a kernfs node with reference counter incremented
+ */
+struct kernfs_node *kernfs_find_and_get_node_by_ino(struct kernfs_root *root,
+ unsigned int ino)
+{
+ struct kernfs_node *kn;
+
+ rcu_read_lock();
+ kn = idr_find(&root->ino_idr, ino);
+ if (!kn)
+ goto out;
+
+ /*
+ * Since kernfs_node is freed in RCU, it's possible an old node for ino
+ * is freed, but reused before RCU grace period. But a freed node (see
+ * kernfs_put) or an incompletedly initialized node (see
+ * __kernfs_new_node) should have 'count' 0. We can use this fact to
+ * filter out such node.
+ */
+ if (!atomic_inc_not_zero(&kn->count)) {
+ kn = NULL;
+ goto out;
+ }
+
+ /*
+ * The node could be a new node or a reused node. If it's a new node,
+ * we are ok. If it's reused because of RCU (because of
+ * SLAB_TYPESAFE_BY_RCU), the __kernfs_new_node always sets its 'ino'
+ * before 'count'. So if 'count' is uptodate, 'ino' should be uptodate,
+ * hence we can use 'ino' to filter stale node.
+ */
+ if (kn->ino != ino)
+ goto out;
+ rcu_read_unlock();
+
+ return kn;
+out:
+ rcu_read_unlock();
+ kernfs_put(kn);
+ return NULL;
+}
+
/**
* kernfs_add_one - add kernfs_node to parent without warning
* @kn: kernfs_node to be added
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