linux-kernel - Re: [PATCH 1/2] srcu: API for barrier after srcu read unlock

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Date:	Wed, 6 Nov 2013 12:00:44 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] srcu: API for barrier after srcu read unlock

On Wed, Nov 06, 2013 at 11:00:21PM +0800, Lai Jiangshan wrote:
> On 11/05/2013 04:55 AM, Paul E. McKenney wrote:
> > On Mon, Nov 04, 2013 at 10:36:17PM +0200, Michael S. Tsirkin wrote:
> >> srcu read lock/unlock include a full memory barrier
> >> but that's an implementation detail.
> >> Add an API for make memory fencing explicit for
> >> users that need this barrier, to make sure we
> >> can change it as needed without breaking all users.
> >>
> >> Acked-by: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> >> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> > 
> > Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 
> Acked-by: "Lai Jiangshan" <laijs@...fujitsu.com>

Very good, queued for 3.14.

							Thanx, Paul

> >> ---
> >>  include/linux/srcu.h | 14 ++++++++++++++
> >>  1 file changed, 14 insertions(+)
> >>
> >> diff --git a/include/linux/srcu.h b/include/linux/srcu.h
> >> index c114614..9b058ee 100644
> >> --- a/include/linux/srcu.h
> >> +++ b/include/linux/srcu.h
> >> @@ -237,4 +237,18 @@ static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
> >>  	__srcu_read_unlock(sp, idx);
> >>  }
> >>
> >> +/**
> >> + * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
> >> + *
> >> + * Converts the preceding srcu_read_unlock into a two-way memory barrier.
> >> + *
> >> + * Call this after srcu_read_unlock, to guarantee that all memory operations
> >> + * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
> >> + * the preceding srcu_read_unlock.
> >> + */
> >> +static inline void smp_mb__after_srcu_read_unlock(void)
> >> +{
> >> +	/* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
> >> +}
> >> +
> >>  #endif
> >> -- 
> >> MST
> >>
> > 
> > --
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> 

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