seq_file: add RCU versions of new hlist/list iterators (v3)

Many usages of seq_file use RCU protected lists, so non RCU
iterators will not work safely.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 87 insertions, 4 deletions

diff --git a/fs/seq_file.c b/fs/seq_file.c
index f65b16f02da3..5afd554efad3 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -750,3 +750,74 @@ struct hlist_node *seq_hlist_next(void *v, struct hlist_head *head,
                 return node->next;
 }
 EXPORT_SYMBOL(seq_hlist_next);
+
+/**
+ * seq_hlist_start_rcu - start an iteration of a hlist protected by RCU
+ * @head: the head of the hlist
+ * @pos:  the start position of the sequence
+ *
+ * Called at seq_file->op->start().
+ *
+ * This list-traversal primitive may safely run concurrently with
+ * the _rcu list-mutation primitives such as hlist_add_head_rcu()
+ * as long as the traversal is guarded by rcu_read_lock().
+ */
+struct hlist_node *seq_hlist_start_rcu(struct hlist_head *head,
+                                       loff_t pos)
+{
+        struct hlist_node *node;
+
+        __hlist_for_each_rcu(node, head)
+                if (pos-- == 0)
+                        return node;
+        return NULL;
+}
+EXPORT_SYMBOL(seq_hlist_start_rcu);
+
+/**
+ * seq_hlist_start_head_rcu - start an iteration of a hlist protected by RCU
+ * @head: the head of the hlist
+ * @pos:  the start position of the sequence
+ *
+ * Called at seq_file->op->start(). Call this function if you want to
+ * print a header at the top of the output.
+ *
+ * This list-traversal primitive may safely run concurrently with
+ * the _rcu list-mutation primitives such as hlist_add_head_rcu()
+ * as long as the traversal is guarded by rcu_read_lock().
+ */
+struct hlist_node *seq_hlist_start_head_rcu(struct hlist_head *head,
+                                            loff_t pos)
+{
+        if (!pos)
+                return SEQ_START_TOKEN;
+
+        return seq_hlist_start_rcu(head, pos - 1);
+}
+EXPORT_SYMBOL(seq_hlist_start_head_rcu);
+
+/**
+ * seq_hlist_next_rcu - move to the next position of the hlist protected by RCU
+ * @v:    the current iterator
+ * @head: the head of the hlist
+ * @pos:  the current posision
+ *
+ * Called at seq_file->op->next().
+ *
+ * This list-traversal primitive may safely run concurrently with
+ * the _rcu list-mutation primitives such as hlist_add_head_rcu()
+ * as long as the traversal is guarded by rcu_read_lock().
+ */
+struct hlist_node *seq_hlist_next_rcu(void *v,
+                                      struct hlist_head *head,
+                                      loff_t *ppos)
+{
+        struct hlist_node *node = v;
+
+        ++*ppos;
+        if (v == SEQ_START_TOKEN)
+                return rcu_dereference(head->first);
+        else
+                return rcu_dereference(node->next);
+}
+EXPORT_SYMBOL(seq_hlist_next_rcu);
diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 1bf0f708c4fc..701fe9cb552a 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -406,6 +406,11 @@ static inline void hlist_add_after_rcu(struct hlist_node *prev,
                 n->next->pprev = &n->next;
 }
 
+#define __hlist_for_each_rcu(pos, head)                 \
+        for (pos = rcu_dereference((head)->first);      \
+             pos && ({ prefetch(pos->next); 1; });      \
+             pos = rcu_dereference(pos->next))
+
 /**
  * hlist_for_each_entry_rcu - iterate over rcu list of given type
  * @tpos:       the type * to use as a loop cursor.
diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
index c95bcdc18f4c..03c0232b4169 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -140,10 +140,17 @@ extern struct list_head *seq_list_next(void *v, struct list_head *head,
  */
 
 extern struct hlist_node *seq_hlist_start(struct hlist_head *head,
-                loff_t pos);
+                                          loff_t pos);
 extern struct hlist_node *seq_hlist_start_head(struct hlist_head *head,
-                loff_t pos);
+                                               loff_t pos);
 extern struct hlist_node *seq_hlist_next(void *v, struct hlist_head *head,
-                loff_t *ppos);
-
+                                         loff_t *ppos);
+
+extern struct hlist_node *seq_hlist_start_rcu(struct hlist_head *head,
+                                              loff_t pos);
+extern struct hlist_node *seq_hlist_start_head_rcu(struct hlist_head *head,
+                                                   loff_t pos);
+extern struct hlist_node *seq_hlist_next_rcu(void *v,
+                                                   struct hlist_head *head,
+                                                   loff_t *ppos);
 #endif