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

[Martin Kepplinger <martin.kepplinger@puri.sm>]

On 04.08.20 11:39, Martin Kepplinger wrote:
> On 30.07.20 17:10, Alan Stern wrote:
>> On Thu, Jul 30, 2020 at 10:52:14AM +0200, Martin Kepplinger wrote:
>>> Maybe I should just start a new discussion with a patch, but the below
>>> is what makes sense to me (when I understand you correctly) and seems to
>>> work. I basically add a new flag, so that the old flags behave unchanged
>>> and only call it during *runtime* resume for SD cards:
>>>
>>>
>>> --- a/drivers/scsi/scsi_error.c
>>> +++ b/drivers/scsi/scsi_error.c
>>> @@ -553,15 +553,21 @@ int scsi_check_sense(struct scsi_cmnd *scmd)
>>>                  * information that we should pass up to the upper-level
>>> driver
>>>                  * so that we can deal with it there.
>>>                  */
>>> -               if (scmd->device->expecting_cc_ua) {
>>> +               if (scmd->device->expecting_cc_ua ||
>>> +                   scmd->device->expecting_media_change) {
>>>                         /*
>>>                          * Because some device does not queue unit
>>>                          * attentions correctly, we carefully check
>>>                          * additional sense code and qualifier so as
>>> -                        * not to squash media change unit attention.
>>> +                        * not to squash media change unit attention;
>>> +                        * unless expecting_media_change is set, indicating
>>> +                        * that the media (most likely) didn't change
>>> +                        * but a device only believes so (for example
>>> +                        * because of suspend/resume).
>>>                          */
>>> -                       if (sshdr.asc != 0x28 || sshdr.ascq != 0x00) {
>>> -                               scmd->device->expecting_cc_ua = 0;
>>> +                       if ((sshdr.asc != 0x28 || sshdr.ascq != 0x00) ||
>>> +                           scmd->device->expecting_media_change) {
>>> +                               scmd->device->expecting_media_change = 0;
>>>                                 return NEEDS_RETRY;
>>>                         }
>>>                 }
>>> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
>>> index d90fefffe31b..b647fab2b663 100644
>>> --- a/drivers/scsi/sd.c
>>> +++ b/drivers/scsi/sd.c
>>> @@ -114,6 +114,7 @@ static void sd_shutdown(struct device *);
>>>  static int sd_suspend_system(struct device *);
>>>  static int sd_suspend_runtime(struct device *);
>>>  static int sd_resume(struct device *);
>>> +static int sd_resume_runtime(struct device *);
>>>  static void sd_rescan(struct device *);
>>>  static blk_status_t sd_init_command(struct scsi_cmnd *SCpnt);
>>>  static void sd_uninit_command(struct scsi_cmnd *SCpnt);
>>> @@ -574,7 +575,7 @@ static const struct dev_pm_ops sd_pm_ops = {
>>>         .poweroff               = sd_suspend_system,
>>>         .restore                = sd_resume,
>>>         .runtime_suspend        = sd_suspend_runtime,
>>> -       .runtime_resume         = sd_resume,
>>> +       .runtime_resume         = sd_resume_runtime,
>>>  };
>>>
>>>  static struct scsi_driver sd_template = {
>>> @@ -3652,6 +3653,21 @@ static int sd_resume(struct device *dev)
>>>         return ret;
>>>  }
>>>
>>> +static int sd_resume_runtime(struct device *dev)
>>> +{
>>> +       struct scsi_disk *sdkp = dev_get_drvdata(dev);
>>> +
>>> +       /* Some SD cardreaders report media change when resuming from
>>> suspend
>>> +        * because they can't keep track during suspend. */
>>> +
>>> +       /* XXX This is not unproblematic though: We won't notice when a card
>>> +        * was really changed during runtime suspend! We basically rely
>>> on users
>>> +        * to unmount or suspend before doing so. */
>>> +       sdkp->device->expecting_media_change = 1;
>>> +
>>> +       return sd_resume(dev);
>>> +}
>>> +
>>>  /**
>>>   *     init_sd - entry point for this driver (both when built in or when
>>>   *     a module).
>>> diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
>>> index bc5909033d13..8c8f053f71c8 100644
>>> --- a/include/scsi/scsi_device.h
>>> +++ b/include/scsi/scsi_device.h
>>> @@ -169,6 +169,8 @@ 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; /* Expecting media change
>>> ASC/ASCQ
>>> +                                             when it actually doesn't
>>> change */
>>>         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 */
>>
>> That's pretty much what James was suggesting, except for one thing: You 
>> must not set sdkp->device->expecting_media_change to 1 for all devices 
>> in sd_runtime_resume().  Only for devices which may generate a spurious 
>> Unit Attention following runtime resume -- and maybe not even for all of 
>> them, depending on what the user wants.
>>
>> Alan Stern
>>
> 
> when I mount the SD card myself or via Nautilus, things work. When I put
> sth like:
> 
> /dev/sda1 /mnt/sda1 auto auto,nofail 0 2
> 
> into fstab, I *still* get (constantly) when accessing the files:
> 
> [   50.838061] sd 0:0:0:0: [sda] tag#0 device offline or changed
> 
> why could that be? is there another place we would add such a new flag
> (not only resume())?
> 
>                               martin
> 


it's really strange: below is the change I'm trying. Of course that's
only for testing the functionality, nothing how a patch could look like.

While I remember it had worked, now (weirdly since I tried that mounting
via fstab) it doesn't anymore!

What I understand (not much): I handle the error with "retry" via the
new flag, but scsi_decide_disposition() returns SUCCESS because of "no
more retries"; but it's the first and only time it's called.

How can this be? What am I missing?



--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -565,6 +565,13 @@ int scsi_check_sense(struct scsi_cmnd *scmd)
 				return NEEDS_RETRY;
 			}
 		}
+		if (scmd->device->expecting_media_change) {
+			if (sshdr.asc == 0x28 && sshdr.ascq == 0x00) {
+				scmd->device->expecting_media_change = 0;
+				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 -
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 */