IB/srp: Avoid that I/O hangs due to a cable pull during LUN scanning

If a cable is pulled during LUN scanning it can happen that the
SRP rport and the SCSI host have been created but no LUNs have been
added to the SCSI host. Since multipathd only sends SCSI commands
to a SCSI target if one or more SCSI devices are present and since
there is no keepalive mechanism for IB queue pairs this means that
after a LUN scan failed and after a reconnect has succeeded no
data will be sent over the QP and hence that a subsequent cable
pull will not be detected. Avoid this by not creating an rport or
SCSI host if a cable is pulled during a SCSI LUN scan.

Note: so far the above behavior has only been observed with the
kernel module parameter ch_count set to a value >= 2.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/infiniband/ulp/srp/ib_srp.c

@@ -1111,6 +1111,10 @@ static int srp_rport_reconnect(struct srp_rport *rport)
 	int i, ret;
 
 	srp_disconnect_target(target);
+
+	if (target->state == SRP_TARGET_SCANNING)
+		return -ENODEV;
+
 	/*
 	 * Now get a new local CM ID so that we avoid confusing the target in
 	 * case things are really fouled up. Doing so also ensures that all CM
@@ -2585,11 +2589,23 @@ static struct scsi_host_template srp_template = {
 	.shost_attrs			= srp_host_attrs
 };
 
+static int srp_sdev_count(struct Scsi_Host *host)
+{
+	struct scsi_device *sdev;
+	int c = 0;
+
+	shost_for_each_device(sdev, host)
+		c++;
+
+	return c;
+}
+
 static int srp_add_target(struct srp_host *host, struct srp_target_port *target)
 {
 	struct srp_rport_identifiers ids;
 	struct srp_rport *rport;
 
+	target->state = SRP_TARGET_SCANNING;
 	sprintf(target->target_name, "SRP.T10:%016llX",
 		 (unsigned long long) be64_to_cpu(target->id_ext));
 
@@ -2612,11 +2628,26 @@ static int srp_add_target(struct srp_host *host, struct srp_target_port *target)
 	list_add_tail(&target->list, &host->target_list);
 	spin_unlock(&host->target_lock);
 
-	target->state = SRP_TARGET_LIVE;
-
 	scsi_scan_target(&target->scsi_host->shost_gendev,
 			 0, target->scsi_id, SCAN_WILD_CARD, 0);
 
+	if (!target->connected || target->qp_in_error) {
+		shost_printk(KERN_INFO, target->scsi_host,
+			     PFX "SCSI scan failed - removing SCSI host\n");
+		srp_queue_remove_work(target);
+		goto out;
+	}
+
+	pr_debug(PFX "%s: SCSI scan succeeded - detected %d LUNs\n",
+		 dev_name(&target->scsi_host->shost_gendev),
+		 srp_sdev_count(target->scsi_host));
+
+	spin_lock_irq(&target->lock);
+	if (target->state == SRP_TARGET_SCANNING)
+		target->state = SRP_TARGET_LIVE;
+	spin_unlock_irq(&target->lock);
+
+out:
 	return 0;
 }
 
@@ -2960,6 +2991,12 @@ static ssize_t srp_create_target(struct device *dev,
 	target->tl_retry_count	= 7;
 	target->queue_size	= SRP_DEFAULT_QUEUE_SIZE;
 
+	/*
+	 * Avoid that the SCSI host can be removed by srp_remove_target()
+	 * before this function returns.
+	 */
+	scsi_host_get(target->scsi_host);
+
 	mutex_lock(&host->add_target_mutex);
 
 	ret = srp_parse_options(buf, target);
@@ -3022,18 +3059,23 @@ static ssize_t srp_create_target(struct device *dev,
 	if (ret)
 		goto err_disconnect;
 
-	shost_printk(KERN_DEBUG, target->scsi_host, PFX
-		     "new target: id_ext %016llx ioc_guid %016llx pkey %04x service_id %016llx sgid %pI6 dgid %pI6\n",
-		     be64_to_cpu(target->id_ext),
-		     be64_to_cpu(target->ioc_guid),
-		     be16_to_cpu(target->path.pkey),
-		     be64_to_cpu(target->service_id),
-		     target->path.sgid.raw, target->path.dgid.raw);
+	if (target->state != SRP_TARGET_REMOVED) {
+		shost_printk(KERN_DEBUG, target->scsi_host, PFX
+			     "new target: id_ext %016llx ioc_guid %016llx pkey %04x service_id %016llx sgid %pI6 dgid %pI6\n",
+			     be64_to_cpu(target->id_ext),
+			     be64_to_cpu(target->ioc_guid),
+			     be16_to_cpu(target->path.pkey),
+			     be64_to_cpu(target->service_id),
+			     target->path.sgid.raw, target->orig_dgid);
+	}
 
 	ret = count;
 
 out:
 	mutex_unlock(&host->add_target_mutex);
+
+	scsi_host_put(target->scsi_host);
+
 	return ret;
 
 err_disconnect:

drivers/infiniband/ulp/srp/ib_srp.h

@@ -73,6 +73,7 @@ enum {
 };
 
 enum srp_target_state {
+	SRP_TARGET_SCANNING,
 	SRP_TARGET_LIVE,
 	SRP_TARGET_REMOVED,
 };