[PATCH] usb-storage: scsiglue: Changing the command result

[Vishal Annapurve]

Hi,

There was a recent commit in mainline for the scsi devices which do not
respond properly to medium access command:

commit    18a4d0a22ed6c54b67af7718c305cd010f09ddf8

[SCSI] Handle disk devices which can not process medium access commands
We have experienced several devices which fail in a fashion we do not
currently handle gracefully in SCSI. After a failure these devices will
respond to the SCSI primary command set (INQUIRY, TEST UNIT READY, etc.)
but any command accessing the storage medium will time out.

I came across a USB drive which showed similar problem and what I see is
usb storage is still not able to cope with such devices properly.

The control flow downwards is like:
scsi_times_out --> Setting cmd->result as DID_TIME_OUT
scsi_error_handler
scsi_unjam_host
scsi_eh_abort_cmds
command_abort    (sets US_FLIDX_TIMED_OUT for us->dflags
                                  calls stop_transport,
                                  and waits for)    usb_stor_control_thread (which is waiting for
                                                                   transport call to return inside
                                                                   usb_stor_invoke_transport)
                                                                   both usb_stor_control_thread and
                                                                   usb_stor_invoke_transport
                                                    check for us->dflags timed_out bit and
                                                     set the result as DID_ABORT
                                                     and signal completion for command_abort
                                                     to complete
......
sd_eh_action
checks for cmd->result and finds out that it's DID_ABORT rather than
DID_TIME_OUT.

This patch updates the command result to be TIME_OUT explicitly before
returning from command_abort in scsiglue.c.

I would like to know if this patch can work out for such USB Storage
devices? What would be the better way to do the same?


Regards,
Vishal Annapurve



From: Vishal Annapurve <vannapurve@xxxxxxxxxx>
Subject: [PATCH] usb-storage: Changing the command result

This change updates the returned result to scsi layer to use
DID_TIMEOUT flag as a result status rather than DID_ABORT for
commands aborted due to timeout.

Signed-off-by: Vishal Annapurve <vannapurve@xxxxxxxxxx>
---
 drivers/usb/storage/scsiglue.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/usb/storage/scsiglue.c b/drivers/usb/storage/scsiglue.c
index a74e9d8..e7b532e 100644
--- a/drivers/usb/storage/scsiglue.c
+++ b/drivers/usb/storage/scsiglue.c
@@ -353,6 +353,15 @@ static int command_abort(struct scsi_cmnd *srb)
 
 	/* Wait for the aborted command to finish */
 	wait_for_completion(&us->notify);
+	/* Given that this bit would be only set in case of timedout
+	 * command, we can return with DID_TIME_OUT, as scsi layer needs
+	 * to use this result rather than DID_ABORT.
+	 * This is a WR to avoid removing DID_ABORT altogether
+	 * and before the final control goes to scsi layer change the
+	 * result to be timedout.
+	 */
+	us->srb->result = DID_TIME_OUT << 16;
+
 	return SUCCESS;
 }
 
-- 
1.8.4