Re: [PATCH] scsi: sd: add runtime pm to open / release

Martin Kepplinger
2020-08-10T12:04:02Z

On 09.08.20 17:26, Alan Stern wrote:
> On Sun, Aug 09, 2020 at 11:20:22AM +0200, Martin Kepplinger wrote:
>> Hey Alan, I'm really glad for that, I suspected some of this but I have
>> little experience in scsi/block layers, so that is super helpful.
>>
>> I'd appreciate an opinion on the below workaround that *seems* to work
>> now (let's see, I had thought so before :)
>>
>> Whether or not this helps to find a real solution, let's see. But
>> integration of such a flag in the error handling paths is what's
>> interesting for now:
>>
>>
>> --- a/drivers/scsi/scsi_error.c
>> +++ b/drivers/scsi/scsi_error.c
>> @@ -565,6 +565,17 @@ int scsi_check_sense(struct scsi_cmnd *scmd)
>> return NEEDS_RETRY;
>> }
>> }
>> + if (scmd->device->expecting_media_change) {
>> + if (sshdr.asc == 0x28 && sshdr.ascq == 0x00) {
>> + /* clear expecting_media_change in
>> + * scsi_noretry_cmd() because we need
>> + * to override possible "failfast" overrides
>> + * that block readahead can cause.
>> + */
>> + return NEEDS_RETRY;
>
> This is a somewhat fragile approach. You don't know for certain that
> scsi_noretry_cmd will be called. Also, scsi_noretry_cmd can be called
> from other places.
>
> It would be better to clear the expecting_media_change flag just before
> returning from scsi_decide_disposition. That way its use is localized
> to one routine, not spread out between two.
>
> Alan Stern
>

Hi Alan,

maybe you're right. I initially just thought that I'd allow for specific
error codes in scsi_noretry_cmd() to return non-NULL (BUS_BUSY, PARITY,
ERROR) despite having the flag set.

The below version works equally fine for me but I'm not sure if it's
actually more safe.

James, when exposing a new writable sysfs option like
"suspend_no_media_change"(?) that drivers can check before setting the
new "expecting_media_change" flag (during resume), would this addition
make sense to you?

thanks,

martin

--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -565,6 +565,18 @@ int scsi_check_sense(struct scsi_cmnd *scmd)
return NEEDS_RETRY;
}
}
+ if (scmd->device->expecting_media_change) {
+ if (sshdr.asc == 0x28 && sshdr.ascq == 0x00) {
+ /*
+ * clear the expecting_media_change in
+ * scsi_decide_disposition() because we
+ * need to catch possible "fail fast" overrides
+ * that block readahead can cause.
+ */
+ return NEEDS_RETRY;
+ }
+ }
+
/*
* we might also expect a cc/ua if another LUN on the target
* reported a UA with an ASC/ASCQ of 3F 0E -
@@ -1944,9 +1956,19 @@ int scsi_decide_disposition(struct scsi_cmnd *scmd)
* the request was not marked fast fail. Note that above,
* even if the request is marked fast fail, we still requeue
* for queue congestion conditions (QUEUE_FULL or BUSY) */
- if ((++scmd->retries) <= scmd->allowed
- && !scsi_noretry_cmd(scmd)) {
- return NEEDS_RETRY;
+ if ((++scmd->retries) <= scmd->allowed) {
+ /*
+ * but scsi_noretry_cmd() cannot override the
+ * expecting_media_change flag.
+ */
+ if (!scsi_noretry_cmd(scmd) ||
+ scmd->device->expecting_media_change) {
+ scmd->device->expecting_media_change = 0;
+ return NEEDS_RETRY;
+ } else {
+ /* marked fast fail and not expected. */
+ return SUCCESS;
+ }
} else {
/*
* no more retries - report this one back to upper level.
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index d90fefffe31b..bb583e403b81 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -3642,6 +3642,8 @@ static int sd_resume(struct device *dev)
if (!sdkp) /* E.g.: runtime resume at the start of sd_probe() */
return 0;

+ sdkp->device->expecting_media_change = 1;
+
if (!sdkp->device->manage_start_stop)
return 0;

diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index bc5909033d13..f5fc1af68e00 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -169,6 +169,7 @@ struct scsi_device {
* this device */
unsigned expecting_cc_ua:1; /* Expecting a CHECK_CONDITION/UNIT_ATTN
* because we did a bus reset. */
+ unsigned expecting_media_change:1;
unsigned use_10_for_rw:1; /* first try 10-byte read / write */
unsigned use_10_for_ms:1; /* first try 10-byte mode sense/select */
unsigned set_dbd_for_ms:1; /* Set "DBD" field in mode sense */
--