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>

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>
stephen hemminger · David S. Miller
1 parent 35e2da46d2
Showing 3 changed files with 87 additions and 4 deletions Side-by-side Diff
fs/seq_file.c
include/linux/rculist.h
include/linux/seq_file.h
@@ -750,4 +750,75 @@
 		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);
@@ -406,6 +406,11 @@
 		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.
@@ -140,11 +140,18 @@
  */
  
 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
...	...	@@ -750,4 +750,75 @@
750	750	return node->next;
751	751	}
752	752	EXPORT_SYMBOL(seq_hlist_next);
	753	+
	754	+/**
	755	+ * seq_hlist_start_rcu - start an iteration of a hlist protected by RCU
	756	+ * @head: the head of the hlist
	757	+ * @pos: the start position of the sequence
	758	+ *
	759	+ * Called at seq_file->op->start().
	760	+ *
	761	+ * This list-traversal primitive may safely run concurrently with
	762	+ * the _rcu list-mutation primitives such as hlist_add_head_rcu()
	763	+ * as long as the traversal is guarded by rcu_read_lock().
	764	+ */
	765	+struct hlist_node seq_hlist_start_rcu(struct hlist_head head,
	766	+ loff_t pos)
	767	+{
	768	+ struct hlist_node *node;
	769	+
	770	+ __hlist_for_each_rcu(node, head)
	771	+ if (pos-- == 0)
	772	+ return node;
	773	+ return NULL;
	774	+}
	775	+EXPORT_SYMBOL(seq_hlist_start_rcu);
	776	+
	777	+/**
	778	+ * seq_hlist_start_head_rcu - start an iteration of a hlist protected by RCU
	779	+ * @head: the head of the hlist
	780	+ * @pos: the start position of the sequence
	781	+ *
	782	+ * Called at seq_file->op->start(). Call this function if you want to
	783	+ * print a header at the top of the output.
	784	+ *
	785	+ * This list-traversal primitive may safely run concurrently with
	786	+ * the _rcu list-mutation primitives such as hlist_add_head_rcu()
	787	+ * as long as the traversal is guarded by rcu_read_lock().
	788	+ */
	789	+struct hlist_node seq_hlist_start_head_rcu(struct hlist_head head,
	790	+ loff_t pos)
	791	+{
	792	+ if (!pos)
	793	+ return SEQ_START_TOKEN;
	794	+
	795	+ return seq_hlist_start_rcu(head, pos - 1);
	796	+}
	797	+EXPORT_SYMBOL(seq_hlist_start_head_rcu);
	798	+
	799	+/**
	800	+ * seq_hlist_next_rcu - move to the next position of the hlist protected by RCU
	801	+ * @v: the current iterator
	802	+ * @head: the head of the hlist
	803	+ * @pos: the current posision
	804	+ *
	805	+ * Called at seq_file->op->next().
	806	+ *
	807	+ * This list-traversal primitive may safely run concurrently with
	808	+ * the _rcu list-mutation primitives such as hlist_add_head_rcu()
	809	+ * as long as the traversal is guarded by rcu_read_lock().
	810	+ */
	811	+struct hlist_node seq_hlist_next_rcu(void v,
	812	+ struct hlist_head *head,
	813	+ loff_t *ppos)
	814	+{
	815	+ struct hlist_node *node = v;
	816	+
	817	+ ++*ppos;
	818	+ if (v == SEQ_START_TOKEN)
	819	+ return rcu_dereference(head->first);
	820	+ else
	821	+ return rcu_dereference(node->next);
	822	+}
	823	+EXPORT_SYMBOL(seq_hlist_next_rcu);
...	...	@@ -406,6 +406,11 @@
406	406	n->next->pprev = &n->next;
407	407	}
408	408
	409	+#define __hlist_for_each_rcu(pos, head) \
	410	+ for (pos = rcu_dereference((head)->first); \
	411	+ pos && ({ prefetch(pos->next); 1; }); \
	412	+ pos = rcu_dereference(pos->next))
	413	+
409	414	/**
410	415	* hlist_for_each_entry_rcu - iterate over rcu list of given type
411	416	* @tpos: the type * to use as a loop cursor.
...	...	@@ -140,11 +140,18 @@
140	140	*/
141	141
142	142	extern struct hlist_node seq_hlist_start(struct hlist_head head,
143		- loff_t pos);
	143	+ loff_t pos);
144	144	extern struct hlist_node seq_hlist_start_head(struct hlist_head head,
145		- loff_t pos);
	145	+ loff_t pos);
146	146	extern struct hlist_node seq_hlist_next(void v, struct hlist_head *head,
147		- loff_t *ppos);
	147	+ loff_t *ppos);
148	148
	149	+extern struct hlist_node seq_hlist_start_rcu(struct hlist_head head,
	150	+ loff_t pos);
	151	+extern struct hlist_node seq_hlist_start_head_rcu(struct hlist_head head,
	152	+ loff_t pos);
	153	+extern struct hlist_node seq_hlist_next_rcu(void v,
	154	+ struct hlist_head *head,
	155	+ loff_t *ppos);
149	156	#endif