Re: [PATCH 07/10] module: __rcu annotations

[Arnd Bergmann <arnd@arndb.de>]

On Wednesday 24 February 2010 23:17:49 Paul E. McKenney wrote:
> > Ok, this is a significant limitation of the list rcu annotation
> > then, it's not possible to pass the same list into list_for_each_entry
> > and list_for_each_entry_rcu with the way I changed the rcu list
> > definition. I would be possible to do a __list_for_each_entry_rcu
> > macro that takes an rcu_list_head but does not actually use
> > rcu_dereference, but I'm not sure if that's good enough.
> 
> Hmmm...  If the __rcu annotation was visible at runtime, it would be
> easy provide an annotated version of list_for_each_entry_rcu() that
> checks for module_mutex being held under lockdep.

Well, if we keep the struct rcu_list_head and make it mandatory for
rcu protected lists, it could be defined as

struct rcu_list_head {
	struct list_head head;
#ifdef CONFIG_PROVE_RCU
	bool (*check)(void);
#endif
};

#ifdef CONFIG_PROVE_RCU
#define RCU_LIST_HEAD_INIT_CHECK(__head, __check) \
	{ .head = LIST_HEAD_INIT((__head).head), .check = (__check) }
#else
#define RCU_LIST_HEAD_INIT_CHECK(__list,__check) {.head = LIST_HEAD_INIT((__head).head) }
#endif

#define RCU_LIST_HEAD_INIT(head) RCU_LIST_HEAD_INIT_CHECK(head,&rcu_read_lock_held)
#define RCU_LIST_HEAD_INIT_BH(head) RCU_LIST_HEAD_INIT_CHECK(head,&rcu_read_lock_bh_held)

#define list_entry_rcu_check(ptr, type, member, check) \
        container_of(rcu_dereference_check((void __rcu __force *)(ptr), check), type, member)

#define list_for_each_entry_rcu(pos, __head, member) \
        for (pos = list_entry_rcu_check((__head)->head.next, typeof(*pos), \
					 member, (__head)->check); \
                prefetch(pos->member.next), &pos->member != (head); \
                pos = list_entry_rcu_check(pos->member.next, typeof(*pos), \
					 member, (__head)->check)))

That would let us check all the heads for correct usage, and at the same
time avoid having to annotate all the list entries.

	Arnd