Re: [PATCH] scsi: core: Fix block I/O error of USB card reader during resume

[Michael Wu]

On 8/17/2022 9:52 PM, Bart Van Assche wrote:
> On 8/17/22 01:34, Michael Wu wrote:
> > When accessing storage device via an USB card reader, a block I/O error
> > occurs during resume:
> >
> > PM: suspend exit
> > sd 0: 0:0:0: [sda] tag#0 UNKNOWN(0x2003) Result: hostbyte=0x00 driverbyte
> > =0x08
> > sd 0: 0:0:0: [sda] tag#0 Sense Key : 0x6 [current]
> > sd 0: 0:0:0: [sda] tag#0 ASC=0x28 ASCQ=0x0
> > sd 0: 0:0:0: [sda] tag#0 CDB: opcode=0x28 28 00 00 17 ce e1 00 00 f0 00
> > blk_update_request: I/O error, dev sda, sector 1560289 op 0x0:(READ) 
> > flags
> > 0x84700 phys_seg 19 prio class 0
> > sd 0: 0:0:0: [sda] tag#0 device offline or changed
> >
> > Fix it by changing the action in scsi_io_completion_action() from
> > ACTION_FAIL to ACTION_RETRY by adding the condition `cmd->device->
> > lockable`.
> >
> > Signed-off-by: Michael Wu <michael@xxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/scsi/scsi_lib.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> > index 4dbd29ab1dcc..4bc480721947 100644
> > --- a/drivers/scsi/scsi_lib.c
> > +++ b/drivers/scsi/scsi_lib.c
> > @@ -704,7 +704,8 @@ static void scsi_io_completion_action(struct 
> > scsi_cmnd *cmd, int result)
> >       } else if (sense_valid && sense_current) {
> >           switch (sshdr.sense_key) {
> >           case UNIT_ATTENTION:
> > -            if (cmd->device->removable) {
> > +            if (cmd->device->removable &&
> > +                cmd->device->lockable) {
> >                   /* Detected disc change.  Set a bit
> >                    * and quietly refuse further access.
> >                    */
>
> To me the above doesn't look like a good way to address this. I don't 
> see why a device being lockable should control whether or not a unit 
> attention results in a retry? Shouldn't the decision taken by 
> scsi_io_completion_action() depend on the ASC and ASCQ codes rather than 
> on whether a device is removable and/or lockable?
Dear Bart,
Yes... My patch did seem suspicious. Here's the scene about the block 
I/O error: Some card reader does not respond the command 'MEDIUM REMOVAL 
PREVENT' correctly, as a result, the host does not send subsequent cmd 
'MEDIUM REMOVAL ALLOW'/'MEDIUM REMOVAL PREVENT' before/after sleep, 
which leads to a enumeration failure after system resume.
I wonder, without changing the behavior of the device, is there's a 
better way to solve this? -- Modifying the scsi core should not be a 
good idea though :(

> BTW, the code modified by the above patch is old. This is what I found 
> in the 2002 version of scsi_lib.c:
>
> if ((SCpnt->sense_buffer[0] & 0x7f) == 0x70
>      && (SCpnt->sense_buffer[2] & 0xf) == UNIT_ATTENTION) {
>          if (SCpnt->device->removable) {
>                  /* detected disc change.  set a bit and quietly refuse
>                   * further access.
>                   */
>                  SCpnt->device->changed = 1;
>                  SCpnt = scsi_end_request(SCpnt, 0, this_count);
>                  return;
>          } else {
>                  /*
>                   * Must have been a power glitch, or a
>                   * bus reset.  Could not have been a
>                   * media change, so we just retry the
>                   * request and see what happens.
>                   */
>                  scsi_queue_next_request(q, SCpnt);
>                  return;
> }
>
> Bart.
>
> Thanks,
Thanks for your kindly notice. I looked around in the latest linux 
mainline repo, but could not find this code. Where can I get this 2002 
version of scsi_lib.c? Thank you.

--
Regards,
Michael Wu