On 09/04/2015 10:00 AM, Bart Van Assche wrote:
> On 09/02/15 07:31, Brian King wrote:
>>
>> This patch fixes an issue seen with an IBM 2145 (SVC) where, following an error
>> injection test which results in paths going offline, when they came
>> back online, the path would timeout the REPORT_LUNS issued during the
>> scan. This timeout situation continued until retries were expired, resulting in
>> falling back to a sequential LUN scan. Then, since the target responds
>> with PQ=1, PDT=0 for all possible LUNs, due to the way the sequential
>> LUN scan code works, we end up adding 512 LUNs for each target, when there
>> is really only a small handful of LUNs that are actually present.
>>
>> This patch doubles the timeout used on the REPORT_LUNS for each retry
>> after a timeout is seen on a REPORT_LUNS. This patch solves the issue
>> of 512 non existent LUNs showing up after this event. Running the test
>> with this patch still showed that we were regularly hitting two timeouts,
>> but the third, and final, REPORT_LUNS was always successful.
>>
>> Signed-off-by: Brian King <brking@xxxxxxxxxxxxxxxxxx>
>> ---
>>
>> drivers/scsi/scsi_scan.c | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff -puN drivers/scsi/scsi_scan.c~scsi_report_luns_timeout_escalate drivers/scsi/scsi_scan.c
>> --- linux/drivers/scsi/scsi_scan.c~scsi_report_luns_timeout_escalate 2015-09-02 08:49:07.268243497 -0500
>> +++ linux-bjking1/drivers/scsi/scsi_scan.c 2015-09-02 08:49:07.272243461 -0500
>> @@ -1304,6 +1304,7 @@ static int scsi_report_lun_scan(struct s
>> struct scsi_device *sdev;
>> struct Scsi_Host *shost = dev_to_shost(&starget->dev);
>> int ret = 0;
>> + int timeout = SCSI_TIMEOUT + 4 * HZ;
>>
>> /*
>> * Only support SCSI-3 and up devices if BLIST_NOREPORTLUN is not set.
>> @@ -1383,7 +1384,7 @@ retry:
>>
>> result = scsi_execute_req(sdev, scsi_cmd, DMA_FROM_DEVICE,
>> lun_data, length, &sshdr,
>> - SCSI_TIMEOUT + 4 * HZ, 3, NULL);
>> + timeout, 3, NULL);
>>
>> SCSI_LOG_SCAN_BUS(3, sdev_printk (KERN_INFO, sdev,
>> "scsi scan: REPORT LUNS"
>> @@ -1392,6 +1393,8 @@ retry:
>> retries, result));
>> if (result == 0)
>> break;
>> + else if (host_byte(result) == DID_TIME_OUT)
>> + timeout = timeout * 2;
>> else if (scsi_sense_valid(&sshdr)) {
>> if (sshdr.sense_key != UNIT_ATTENTION)
>> break;
>
> This is somewhat of a hack, but anyway:
>
> Reviewed-by: Bart Van Assche <bvanassche@xxxxxxxxxxx>
Agreed.
Thanks for the review.
-Brian
--
Brian King
Power Linux I/O
IBM Linux Technology Center
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