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Commit 1658d35e authored Sep 20, 2015 by Paul E. McKenney

list: Use READ_ONCE() when testing for empty lists



Most of the list-empty-check macros (list_empty(), hlist_empty(),
hlist_bl_empty(), hlist_nulls_empty(), and hlist_nulls_empty()) use
an unadorned load to check the list header.  Given that these macros
are sometimes invoked without the protection of a lock, this is
not sufficient.  This commit therefore adds READ_ONCE() calls to
them.  This commit does not touch llist_empty() because it already
has the needed ACCESS_ONCE().

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

parent 1c97be67

include/linux/list.h

+2 −2

Original line number	Original line	Diff line number	Diff line
	@@ -186,7 +186,7 @@ static inline int list_is_last(const struct list_head *list,
	*/		*/
	static inline int list_empty(const struct list_head *head)		static inline int list_empty(const struct list_head *head)
	{		{
	return head->next == head;		return READ_ONCE(head->next) == head;
	}		}

	/**		/**
	@@ -608,7 +608,7 @@ static inline int hlist_unhashed(const struct hlist_node *h)

	static inline int hlist_empty(const struct hlist_head *h)		static inline int hlist_empty(const struct hlist_head *h)
	{		{
	return !h->first;		return !READ_ONCE(h->first);
	}		}

	static inline void __hlist_del(struct hlist_node *n)		static inline void __hlist_del(struct hlist_node *n)

include/linux/list_bl.h

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -70,7 +70,7 @@ static inline void hlist_bl_set_first(struct hlist_bl_head *h,

	static inline int hlist_bl_empty(const struct hlist_bl_head *h)		static inline int hlist_bl_empty(const struct hlist_bl_head *h)
	{		{
	return !((unsigned long)h->first & ~LIST_BL_LOCKMASK);		return !((unsigned long)READ_ONCE(h->first) & ~LIST_BL_LOCKMASK);
	}		}

	static inline void hlist_bl_add_head(struct hlist_bl_node *n,		static inline void hlist_bl_add_head(struct hlist_bl_node *n,

include/linux/list_nulls.h

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -57,7 +57,7 @@ static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)

	static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)		static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
	{		{
	return is_a_nulls(h->first);		return is_a_nulls(READ_ONCE(h->first));
	}		}

	static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,		static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,