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

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Date:	Wed, 06 Nov 2013 23:00:21 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	paulmck@...ux.vnet.ibm.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 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>

> 
>> ---
>>  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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