Commit-ID: 1658d35ead5d8dd76f2b2d6ad0e32c08d123faa2
Gitweb: http://git.kernel.org/tip/1658d35ead5d8dd76f2b2d6ad0e32c08d123faa2
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Sun, 20 Sep 2015 17:03:16 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Mon, 23 Nov 2015 10:37:35 -0800
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@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
include/linux/list.h | 4 ++--
include/linux/list_bl.h | 2 +-
include/linux/list_nulls.h | 2 +-
3 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/include/linux/list.h b/include/linux/list.h
index d7e31fe..06c2d88 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -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)
{
- 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)
{
- return !h->first;
+ return !READ_ONCE(h->first);
}
static inline void __hlist_del(struct hlist_node *n)
diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h
index 8132214..ee7229a 100644
--- a/include/linux/list_bl.h
+++ b/include/linux/list_bl.h
@@ -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)
{
- 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,
diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h
index 444d2b1..b01fe10 100644
--- a/include/linux/list_nulls.h
+++ b/include/linux/list_nulls.h
@@ -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)
{
- 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,
--
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