Commit 7f5f873c authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rculist: Use WRITE_ONCE() when deleting from reader-visible list 



The various RCU list-deletion macros (list_del_rcu(),
hlist_del_init_rcu(), hlist_del_rcu(), hlist_bl_del_init_rcu(),
hlist_bl_del_rcu(), hlist_nulls_del_init_rcu(), and hlist_nulls_del_rcu())
do plain stores into the ->next pointer of the preceding list elemment.
Unfortunately, the compiler is within its rights to (for example) use
byte-at-a-time writes to update the pointer, which would fatally confuse
concurrent readers.  This patch therefore adds the needed WRITE_ONCE()
macros.

KernelThreadSanitizer (KTSAN) reported the __hlist_del() issue, which
is a problem when __hlist_del() is invoked by hlist_del_rcu().

Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
parent e62e3f62

include/linux/list.h

+3 −2
Original line number Diff line number Diff line
@@ -87,7 +87,7 @@ static inline void list_add_tail(struct list_head *new, struct list_head *head) 
static inline void __list_del(struct list_head * prev, struct list_head * next)

{

	next->prev = prev;

	prev->next = next;

	WRITE_ONCE(prev->next, next);

}



/**
@@ -615,7 +615,8 @@ static inline void __hlist_del(struct hlist_node *n) 
{

	struct hlist_node *next = n->next;

	struct hlist_node **pprev = n->pprev;

	*pprev = next;



	WRITE_ONCE(*pprev, next);

	if (next)

		next->pprev = pprev;

}

include/linux/list_bl.h

+3 −2
Original line number Diff line number Diff line
@@ -93,9 +93,10 @@ static inline void __hlist_bl_del(struct hlist_bl_node *n) 
	LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);



	/* pprev may be `first`, so be careful not to lose the lock bit */

	*pprev = (struct hlist_bl_node *)

	WRITE_ONCE(*pprev,

		   (struct hlist_bl_node *)

			((unsigned long)next |

			 ((unsigned long)*pprev & LIST_BL_LOCKMASK));

			 ((unsigned long)*pprev & LIST_BL_LOCKMASK)));

	if (next)

		next->pprev = pprev;

}

include/linux/list_nulls.h

+2 −1
Original line number Diff line number Diff line
@@ -76,7 +76,8 @@ static inline void __hlist_nulls_del(struct hlist_nulls_node *n) 
{

	struct hlist_nulls_node *next = n->next;

	struct hlist_nulls_node **pprev = n->pprev;

	*pprev = next;



	WRITE_ONCE(*pprev, next);

	if (!is_a_nulls(next))

		next->pprev = pprev;

}

CRA Git | Maintained and supported by SUSTech CRA and CCSE