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

Alan Stern
2020-08-10T14:13:48Z

On Mon, Aug 10, 2020 at 02:03:17PM +0200, Martin Kepplinger wrote:
> On 09.08.20 17:26, Alan Stern wrote:
> > 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 {

This may not matter... but it's worth pointing out that
expecting_media_change doesn't get cleared if ++scmd->retries >
scmd->allowed.

It also doesn't get cleared in cases where the device _doesn't_
report a Unit Attention.

Alan Stern