[PATCH] libata: implement ata_scsi_timed_out()

Implement ata_scsi_timed_out(), to be used as
scsi_host_template->eh_timed_out callback for all libata drivers.
Without this function, the following race exists.

If a qc completes after SCSI timer expires but before libata EH kicks
in, the qc gets completed but the scsicmd still gets passed to libata
EH resulting in ->eng_timeout invocation with NULL qc, which none is
handling properly.

This patch makes sure that scmd and qc share the same lifetime.
Original idea from Jeff Garzik <jgarzik@pobox.com>.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>

1 files changed, 41 insertions, 0 deletions

diff --git a/drivers/scsi/libata-scsi.c b/drivers/scsi/libata-scsi.c
index 1df468eb2bf..d67cc2fb569 100644
--- a/drivers/scsi/libata-scsi.c
+++ b/drivers/scsi/libata-scsi.c
@@ -717,6 +717,47 @@ int ata_scsi_slave_config(struct scsi_device *sdev)
 }
 
 /**
+ *      ata_scsi_timed_out - SCSI layer time out callback
+ *      @cmd: timed out SCSI command
+ *
+ *      Handles SCSI layer timeout.  We race with normal completion of
+ *      the qc for @cmd.  If the qc is already gone, we lose and let
+ *      the scsi command finish (EH_HANDLED).  Otherwise, the qc has
+ *      timed out and EH should be invoked.  Prevent ata_qc_complete()
+ *      from finishing it by setting EH_SCHEDULED and return
+ *      EH_NOT_HANDLED.
+ *
+ *      LOCKING:
+ *      Called from timer context
+ *
+ *      RETURNS:
+ *      EH_HANDLED or EH_NOT_HANDLED
+ */
+enum scsi_eh_timer_return ata_scsi_timed_out(struct scsi_cmnd *cmd)
+{
+        struct Scsi_Host *host = cmd->device->host;
+        struct ata_port *ap = (struct ata_port *) &host->hostdata[0];
+        unsigned long flags;
+        struct ata_queued_cmd *qc;
+        enum scsi_eh_timer_return ret = EH_HANDLED;
+
+        DPRINTK("ENTER\n");
+
+        spin_lock_irqsave(&ap->host_set->lock, flags);
+        qc = ata_qc_from_tag(ap, ap->active_tag);
+        if (qc) {
+                assert(qc->scsicmd == cmd);
+                qc->flags |= ATA_QCFLAG_EH_SCHEDULED;
+                qc->err_mask |= AC_ERR_TIMEOUT;
+                ret = EH_NOT_HANDLED;
+        }
+        spin_unlock_irqrestore(&ap->host_set->lock, flags);
+
+        DPRINTK("EXIT, ret=%d\n", ret);
+        return ret;
+}
+
+/**
  *      ata_scsi_error - SCSI layer error handler callback
  *      @host: SCSI host on which error occurred
  *