[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>

1 files changed, 13 insertions, 0 deletions

diff --git a/drivers/scsi/libata-scsi.c b/drivers/scsi/libata-scsi.c
index 7ced41ecde86..e92c31d698ff 100644
--- a/drivers/scsi/libata-scsi.c
+++ b/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);