[dm-devel] [PATCH] Remove capping from dev_loss_tmo

[Hannes Reinecke]

Currently dev_loss_tmo is capped by SCSI_DEVICE_BLOCK_MAX_TIMEOUT.
This causes problem with multipathing when the 'no_path_retry' setting
exceeds the dev_loss_tmo setting, as then the system might run into
a deadlock when all paths have been removed temporarily for longer
than dev_loss_tmo.
The principal reasons for the capping has been that we should
not allow a remote port to remain in status 'blocked' indefinitely,
so the capping is there to ensure that the port status is being reset
eventually.
However, the fast_io_fail_tmo will also move the remote port out of
the 'blocked' state, so for any HBA driver implementing both the
capping should really be on the fast_io_fail_tmo, and not on the
dev_loss_tmo.
This patch implements just that, ie the fast_io_fail_tmo is capped
to SCSI_DEVICE_BLOCK_TIMEOUT and the capping is removed from
dev_loss_tmo when fast_io_fail_tmo is set.
This allows us to synchronize the dev_loss_tmo setting to the
'no_path_retry' setting from multipathing thus avoiding the deadlock.

Signed-off-by: Hannes Reinecke <hare at suse.de>

diff --git a/drivers/scsi/scsi_transport_fc.c b/drivers/scsi/scsi_transport_fc.c
index 573ce21..6f39bf4 100644
--- a/drivers/scsi/scsi_transport_fc.c
+++ b/drivers/scsi/scsi_transport_fc.c
@@ -475,7 +475,8 @@ MODULE_PARM_DESC(dev_loss_tmo,
 		 "Maximum number of seconds that the FC transport should"
 		 " insulate the loss of a remote port. Once this value is"
 		 " exceeded, the scsi target is removed. Value should be"
-		 " between 1 and SCSI_DEVICE_BLOCK_MAX_TIMEOUT.");
+		 " between 1 and SCSI_DEVICE_BLOCK_MAX_TIMEOUT if"
+		 " fast_io_fail_tmo is not set.");
 
 /*
  * Netlink Infrastructure
@@ -831,9 +832,17 @@ store_fc_rport_dev_loss_tmo(struct device *dev, struct device_attribute *attr,
 	    (rport->port_state == FC_PORTSTATE_NOTPRESENT))
 		return -EBUSY;
 	val = simple_strtoul(buf, &cp, 0);
-	if ((*cp && (*cp != '\n')) ||
-	    (val < 0) || (val > SCSI_DEVICE_BLOCK_MAX_TIMEOUT))
+	if ((*cp && (*cp != '\n')) || (val < 0))
 		return -EINVAL;
+
+	/*
+	 * If fast_io_fail is off we have to cap
+	 * dev_loss_tmo at SCSI_DEVICE_BLOCK_MAX_TIMEOUT
+	 */
+	if (rport->fast_io_fail_tmo == -1 &&
+	    val > SCSI_DEVICE_BLOCK_MAX_TIMEOUT)
+		return -EINVAL;
+
 	i->f->set_rport_dev_loss_tmo(rport, val);
 	return count;
 }
@@ -914,9 +923,16 @@ store_fc_rport_fast_io_fail_tmo(struct device *dev,
 		rport->fast_io_fail_tmo = -1;
 	else {
 		val = simple_strtoul(buf, &cp, 0);
-		if ((*cp && (*cp != '\n')) ||
-		    (val < 0) || (val >= rport->dev_loss_tmo))
+		if ((*cp && (*cp != '\n')) || (val < 0))
 			return -EINVAL;
+		/*
+		 * Cap fast_io_fail by dev_loss_tmo or
+		 * SCSI_DEVICE_BLOCK_MAX_TIMEOUT.
+		 */
+		if ((val >= rport->dev_loss_tmo) ||
+		    (val > SCSI_DEVICE_BLOCK_MAX_TIMEOUT))
+			return -EINVAL;
+
 		rport->fast_io_fail_tmo = val;
 	}
 	return count;