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Date:	Wed, 23 Jul 2014 10:10:38 +0800
From:	Mike Qiu <qiudayu@...ux.vnet.ibm.com>
To:	Tejun Heo <tj@...nel.org>
CC:	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	haokexin@...il.com, Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH 1/2] libata: Fix scsi_host can_queue issue in ata_qc_new()

On 07/22/2014 11:42 PM, Tejun Heo wrote:
> Hello,
>
> (cc'ing Dan)
>
> On Tue, Jul 22, 2014 at 10:50:19AM -0400, Mike Qiu wrote:
>> The can_queue in scsi_host can be more than ATA_MAX_QUEUE (32),
>> for example, in ipr, it can be 100 or more.
>>
>> Also, some drivers, like ipr driver, haven't filled the field
>> scsi_host in ata_port, and will lead a call trace, so add
>> check for that.
>>
>> Signed-off-by: Mike Qiu <qiudayu@...ux.vnet.ibm.com>
>> ---
>>   drivers/ata/libata-core.c | 15 ++++-----------
>>   1 file changed, 4 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
>> index 259d879..a5b9c70 100644
>> --- a/drivers/ata/libata-core.c
>> +++ b/drivers/ata/libata-core.c
>> @@ -4734,7 +4734,10 @@ static struct ata_queued_cmd *ata_qc_new(struct ata_port *ap)
>>   	struct ata_queued_cmd *qc = NULL;
>>   	unsigned int i, tag, max_queue;
>>   
>> -	max_queue = ap->scsi_host->can_queue;
>> +	if (ap->scsi_host && ap->scsi_host->can_queue <= ATA_MAX_QUEUE)
>> +		max_queue = ap->scsi_host->can_queue;
>> +	else
>> +		max_queue = ATA_MAX_QUEUE;
>>   
>>   	/* no command while frozen */
>>   	if (unlikely(ap->pflags & ATA_PFLAG_FROZEN))
>> @@ -6109,16 +6112,6 @@ int ata_host_register(struct ata_host *host, struct scsi_host_template *sht)
>>   {
>>   	int i, rc;
>>   
>> -	/*
>> -	 * The max queue supported by hardware must not be greater than
>> -	 * ATA_MAX_QUEUE.
>> -	 */
>> -	if (sht->can_queue > ATA_MAX_QUEUE) {
>> -		dev_err(host->dev, "BUG: the hardware max queue is too large\n");
>> -		WARN_ON(1);
>> -		return -EINVAL;
>> -	}
>> -
> So, ummm, I really don't like that we're adding the conditionals to
> the hot path (yeah, its implementation is slow but still).  Maybe we

Yes, agree ..., not a good idea to do this...

Thanks
Mike
> need to store the chosen queue depth after all?  Dan?
>
> Thanks.
>

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