On Tue, Oct 06, 2015 at 09:13:45AM -0700, Paul E. McKenney wrote:
> This commit adds an rcu_pointer_handoff() that is intended to mark
> situations where a structure's protection transitions from RCU to some
> other mechanism (locking, reference counting, whatever). These markings
> should allow external tools to more easily spot bugs involving leaking
> pointers out of RCU read-side critical sections.
>
> Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Shouldn't this expect the __rcu address space on the pointer, and cast
away the __rcu with __force?
> include/linux/rcupdate.h | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 6c3ceceb6148..587eb057e2fa 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -813,6 +813,28 @@ static inline void rcu_preempt_sleep_check(void)
> #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
>
> /**
> + * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
> + * @p: The pointer to hand off
> + *
> + * This is simply an identity function, but it documents where a pointer
> + * is handed off from RCU to some other synchronization mechanism, for
> + * example, reference counting or locking. In C11, it would map to
> + * kill_dependency(). It could be used as follows:
> + *
> + * rcu_read_lock();
> + * p = rcu_dereference(gp);
> + * long_lived = is_long_lived(p);
> + * if (long_lived) {
> + * if (!atomic_inc_not_zero(p->refcnt))
> + * long_lived = false;
> + * else
> + * p = rcu_pointer_handoff(p);
> + * }
> + * rcu_read_unlock();
> + */
> +#define rcu_pointer_handoff(p) (p)
> +
> +/**
> * rcu_read_lock() - mark the beginning of an RCU read-side critical section
> *
> * When synchronize_rcu() is invoked on one CPU while other CPUs
> --
> 2.5.2
>
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