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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 <dvyukov@google.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
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@ -87,7 +87,7 @@ static inline void list_add_tail(struct list_head *new, struct list_head *head)
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static inline void __list_del(struct list_head * prev, struct list_head * next)
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{
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next->prev = prev;
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prev->next = next;
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WRITE_ONCE(prev->next, next);
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}
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/**
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@ -615,7 +615,8 @@ static inline void __hlist_del(struct hlist_node *n)
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{
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struct hlist_node *next = n->next;
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struct hlist_node **pprev = n->pprev;
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*pprev = next;
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WRITE_ONCE(*pprev, next);
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if (next)
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next->pprev = pprev;
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}
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@ -93,9 +93,10 @@ static inline void __hlist_bl_del(struct hlist_bl_node *n)
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LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);
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/* pprev may be `first`, so be careful not to lose the lock bit */
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*pprev = (struct hlist_bl_node *)
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WRITE_ONCE(*pprev,
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(struct hlist_bl_node *)
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((unsigned long)next |
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((unsigned long)*pprev & LIST_BL_LOCKMASK));
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((unsigned long)*pprev & LIST_BL_LOCKMASK)));
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if (next)
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next->pprev = pprev;
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}
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@ -76,7 +76,8 @@ static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
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{
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struct hlist_nulls_node *next = n->next;
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struct hlist_nulls_node **pprev = n->pprev;
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*pprev = next;
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WRITE_ONCE(*pprev, next);
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if (!is_a_nulls(next))
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next->pprev = pprev;
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}
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