Re: [PATCH 6/6] rcusync: Introduce rcu_sync_dtor()

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Tue, Oct 08, 2013 at 12:25:11PM +0200, Peter Zijlstra wrote:
> From: Oleg Nesterov <oleg@redhat.com>
> 
> Add the new rcu_sync_ops->wait() method and the new helper,
> rcu_sync_dtor().
> 
> It is needed if you are going to, say, kfree(rcu_sync_object).
> It simply calls ops->wait() to "flush" the potentially pending
> rcu callback.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> Signed-off-by: Peter Zijlstra <peterz@infradead.org>

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> Link: http://lkml.kernel.org/r/20131004184636.GA17560@redhat.com
> ---
>  include/linux/rcusync.h |    1 +
>  kernel/rcusync.c        |   22 ++++++++++++++++++++++
>  2 files changed, 23 insertions(+)
> 
> --- a/include/linux/rcusync.h
> +++ b/include/linux/rcusync.h
> @@ -31,6 +31,7 @@ static inline bool rcu_sync_is_idle(stru
>  extern void rcu_sync_init(struct rcu_sync_struct *, enum rcu_sync_type);
>  extern void rcu_sync_enter(struct rcu_sync_struct *);
>  extern void rcu_sync_exit(struct rcu_sync_struct *);
> +extern void rcu_sync_dtor(struct rcu_sync_struct *);
> 
>  #define __RCU_SYNC_INITIALIZER(name, type) {				\
>  		.gp_state = 0,						\
> --- a/kernel/rcusync.c
> +++ b/kernel/rcusync.c
> @@ -10,6 +10,7 @@
>  static const struct {
>  	void (*sync)(void);
>  	void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
> +	void (*wait)(void);
>  #ifdef CONFIG_PROVE_RCU
>  	int  (*held)(void);
>  #endif
> @@ -17,16 +18,19 @@ static const struct {
>  	[RCU_SYNC] = {
>  		.sync = synchronize_rcu,
>  		.call = call_rcu,
> +		.wait = rcu_barrier,
>  		__INIT_HELD(rcu_read_lock_held)
>  	},
>  	[RCU_SCHED_SYNC] = {
>  		.sync = synchronize_sched,
>  		.call = call_rcu_sched,
> +		.wait = rcu_barrier_sched,
>  		__INIT_HELD(rcu_read_lock_sched_held)
>  	},
>  	[RCU_BH_SYNC] = {
>  		.sync = synchronize_rcu_bh,
>  		.call = call_rcu_bh,
> +		.wait = rcu_barrier_bh,
>  		__INIT_HELD(rcu_read_lock_bh_held)
>  	},
>  };
> @@ -128,3 +132,21 @@ void rcu_sync_exit(struct rcu_sync_struc
>  	}
>  	spin_unlock_irq(&rss->rss_lock);
>  }
> +
> +void rcu_sync_dtor(struct rcu_sync_struct *rss)
> +{
> +	int cb_state;
> +
> +	BUG_ON(rss->gp_count);
> +
> +	spin_lock_irq(&rss->rss_lock);
> +	if (rss->cb_state == CB_REPLAY)
> +		rss->cb_state = CB_PENDING;
> +	cb_state = rss->cb_state;
> +	spin_unlock_irq(&rss->rss_lock);
> +
> +	if (cb_state != CB_IDLE) {
> +		gp_ops[rss->gp_type].wait();
> +		BUG_ON(rss->cb_state != CB_IDLE);
> +	}
> +}
> 
>