rculist: Add hlists_swap_heads_rcu (35fc0e3b) · Commits · 戴 / test

Using the struct pid to refer to two tasks in de_thread was a clever idea and ultimately too clever, as it has lead to proc_flush_task being called inconsistently. To support rectifying this add hlists_swap_heads_rcu. An hlist primitive that just swaps the hlist heads of two lists. This is exactly what is needed for exchanging the pids of two tasks. Only consideration of correctness of the code has been given, as the caller is expected to be a slowpath. Link: https://lore.kernel.org/lkml/87mu6vajnq.fsf_-_@x220.int.ebiederm.org/ Acked-by:

Linus Torvalds <torvalds@linux-foundation.org> Acked-by:

Oleg Nesterov <oleg@redhat.com> Signed-off-by:

"Eric W. Biederman" <ebiederm@xmission.com>

include/linux/rculist.h

+21 −0

Original line number	Diff line number	Diff line
		@@ -506,6 +506,27 @@ static inline void hlist_replace_rcu(struct hlist_node *old,
		WRITE_ONCE(old->pprev, LIST_POISON2);
		}

		/**
		* hlists_swap_heads_rcu - swap the lists the hlist heads point to
		* @left: The hlist head on the left
		* @right: The hlist head on the right
		*
		* The lists start out as [@left ][node1 ... ] and
		[@right ][node2 ... ]
		* The lists end up as [@left ][node2 ... ]
		* [@right ][node1 ... ]
		*/
		static inline void hlists_swap_heads_rcu(struct hlist_head left, struct hlist_head right)
		{
		struct hlist_node *node1 = left->first;
		struct hlist_node *node2 = right->first;

		rcu_assign_pointer(left->first, node2);
		rcu_assign_pointer(right->first, node1);
		WRITE_ONCE(node2->pprev, &left->first);
		WRITE_ONCE(node1->pprev, &right->first);
		}

		/*
		* return the first or the next element in an RCU protected hlist
		*/

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