From 7f5f873c6a0772970d5fee1f364231207051ecd8 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 18 Sep 2015 08:45:22 -0700 Subject: 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: Dmitry Vyukov Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- include/linux/list_bl.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'include/linux/list_bl.h') diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h index 2eb88556c5c5..8132214e8efd 100644 --- a/include/linux/list_bl.h +++ b/include/linux/list_bl.h @@ -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; } -- cgit