[PATCH] libata: clear sdev->locked on door lock failure

SCSI EH locks door if sdev->locked is set.  Sometimes door lock
command fails continuously (e.g. when medium is not present) and as
libata uses EH to acquire sense data, this easily creates a loop where
a failed lock door invokes EH and EH issues lock door on completion.

This patch clears sdev->locked on door lock failure to break this
loop.  This problem has been spotted and diagnosed by Unicorn Chang
<uchang@tw.ibm.com>.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/scsi/libata-scsi.c

@@ -2353,6 +2353,19 @@ static void atapi_qc_complete(struct ata_queued_cmd *qc)
 			ata_gen_ata_desc_sense(qc);
 		}
 
+		/* SCSI EH automatically locks door if sdev->locked is
+		 * set.  Sometimes door lock request continues to
+		 * fail, for example, when no media is present.  This
+		 * creates a loop - SCSI EH issues door lock which
+		 * fails and gets invoked again to acquire sense data
+		 * for the failed command.
+		 *
+		 * If door lock fails, always clear sdev->locked to
+		 * avoid this infinite loop.
+		 */
+		if (qc->cdb[0] == ALLOW_MEDIUM_REMOVAL)
+			qc->dev->sdev->locked = 0;
+
 		qc->scsicmd->result = SAM_STAT_CHECK_CONDITION;
 		qc->scsidone(cmd);
 		ata_qc_free(qc);