On 09/04/2015 11:15 AM, James Bottomley wrote:
> On Fri, 2015-09-04 at 10:47 -0500, Brian King wrote:
>> On 09/04/2015 10:36 AM, James Bottomley wrote:
>>> On Wed, 2015-09-02 at 09:31 -0500, 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)
>>>
>>> Actually, this is a bit pointless, isn't it; why retry, why not just set
>>> the initial timeout? ... I could understand if retrying and printing a
>>> message gave important or useful information, but it doesn't. How long
>>> do you actually need? ... we can just up the initial timeout to that.
>>> Currently we have a hacked 6s which looks arbitrary. Would 15s be
>>> better? Nothing really times out anyway, so everything else will still
>>> reply within the original 6s giving zero impact in the everyday case.
>>
>> 12 seconds definitely isn't long enough, but 24 seconds seems to work, at least
>> after we go through both a 6 and 12 second timeout. Anyone opposed to using 30 seconds?
>> 15 seconds is likely to be right on the edge in this scenario.
>
> 30s is fine by me. I think the initial 2s was from the sequential
> inquiry scan so as not to wait too long. The extra 4s was added because
> that was too short for report luns on some devices; I suspect some
> larger arrays take a while just to gather all the data.
>
> 30s is also the traditional rq_timeout, so it may be possible to re-use
> this parameter. Currently it's set up in the ULD, so it's zero unless
> the slave_configure requested a special value. Traditionally, it's the
> timeout for _READ and _WRITE, not special commands, but it feels like
> REPORT_LUNS should follow this timeout as well and it would give you a
> configurable way of updating it in your driver. If we do it this way,
> you'd have to set it in slave_alloc, because slave_configure is too
> late.
I think we may just need to hard code it like the patch below. Here is the current flow for
setting this today:
slave_alloc
scsi scan: inquiry / report LUNs
slave_configure
sd attach
Some LLDDs set a default timeout in slave_configure today, so sd.c only sets a default timeout
if its not already set. It uses 30 seconds for disks and 75 seconds for optical devices.
If we start setting rq_timeout earlier, then the ULD will never know when it can set it.
Additionally, in this particular scenario, its not so much a case of behavior tied to the LLDD, its more tied
to the SCSI target. If there is concern about increasing the default to 30 seconds, we could
use a blist attribute for this.
-Brian
8<
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 increases the timeout used on the REPORT_LUNS to 30 seconds.
This patch solves the issue of 512 non existent LUNs showing up after
this event.
Signed-off-by: Brian King <brking@xxxxxxxxxxxxxxxxxx>
---
drivers/scsi/scsi_scan.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff -puN drivers/scsi/scsi_scan.c~scsi_report_luns_30secs drivers/scsi/scsi_scan.c
--- linux/drivers/scsi/scsi_scan.c~scsi_report_luns_30secs 2015-09-04 14:38:47.890757391 -0500
+++ linux-bjking1/drivers/scsi/scsi_scan.c 2015-09-04 14:39:28.891459147 -0500
@@ -55,6 +55,7 @@
* Default timeout
*/
#define SCSI_TIMEOUT (2*HZ)
+#define SCSI_REPORT_LUNS_TIMEOUT (30*HZ)
/*
* Prefix values for the SCSI id's (stored in sysfs name field)
@@ -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);
+ SCSI_REPORT_LUNS_TIMEOUT, 3, NULL);
SCSI_LOG_SCAN_BUS(3, sdev_printk (KERN_INFO, sdev,
"scsi scan: REPORT LUNS"
_
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