Re: [PATCH] ibmvscsi: add write memory barrier to CRQ processing

[Tyrel Datwyler <turtle.in.the.kernel@gmail.com>]

On 12/08/2016 03:29 PM, Paolo Bonzini wrote:
> 
> 
> On 08/12/2016 00:31, Tyrel Datwyler wrote:
>> The first byte of each CRQ entry is used to indicate whether an entry is
>> a valid response or free for the VIOS to use. After processing a
>> response the driver sets the valid byte to zero to indicate the entry is
>> now free to be reused. Add a memory barrier after this write to ensure
>> no other stores are reordered when updating the valid byte.
>>
>> Signed-off-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
>> ---
>>  drivers/scsi/ibmvscsi/ibmvscsi.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/scsi/ibmvscsi/ibmvscsi.c b/drivers/scsi/ibmvscsi/ibmvscsi.c
>> index d9534ee..2f5b07e 100644
>> --- a/drivers/scsi/ibmvscsi/ibmvscsi.c
>> +++ b/drivers/scsi/ibmvscsi/ibmvscsi.c
>> @@ -232,6 +232,7 @@ static void ibmvscsi_task(void *data)
>>  		while ((crq = crq_queue_next_crq(&hostdata->queue)) != NULL) {
>>  			ibmvscsi_handle_crq(crq, hostdata);
>>  			crq->valid = VIOSRP_CRQ_FREE;
>> +			wmb();
>>  		}
>>  
>>  		vio_enable_interrupts(vdev);
>> @@ -240,6 +241,7 @@ static void ibmvscsi_task(void *data)
>>  			vio_disable_interrupts(vdev);
>>  			ibmvscsi_handle_crq(crq, hostdata);
>>  			crq->valid = VIOSRP_CRQ_FREE;
>> +			wmb();
> 
> Should this driver use virt_wmb instead?

Both virt_wmb and wmb reduce to a lwsync instruction under PowerPC.

-Tyrel

> 
> Paolo
> 
>>  		} else {
>>  			done = 1;
>>  		}
>>