[SCSI] scsi_dh_rdac: Fix for unbalanced reference count

This patch fixes an unbalanced refcount issue.

Elevating the lock for both kref_put and also for controller node deletion.
Previously, controller deletion was protected but the not the kref_put. This
was causing the other thread to pick up the controller structure which was
already kref'd zero.

This was causing the following WARN_ON and also sometimes panic.

WARNING: at lib/kref.c:43 kref_get+0x2d/0x30() (Not tainted)
Hardware name: IBM System x3655 -[7985AC1]-
Modules linked in: fuse scsi_dh_rdac autofs4 nfs lockd fscache nfs_acl
auth_rpcgss sunrpc 8021q garp stp llc ipv6 ib_srp(U) scsi_transport_srp
scsi_tgt ib_cm(U) ib_sa(U) ib_uverbs(U) ib_umad(U) mlx4_ib(U) mlx4_core(U)
ib_mthca(U) ib_mad(U) ib_core(U) dm_mirror dm_region_hash dm_log dm_round_robin
dm_multipath uinput bnx2 ses enclosure sg ibmpex ibmaem ipmi_msghandler
serio_raw k8temp hwmon amd64_edac_mod edac_core edac_mce_amd shpchp i2c_piix4
ext4 mbcache jbd2 sr_mod cdrom sd_mod crc_t10dif sata_svw pata_acpi ata_generic
pata_serverworks aacraid radeon ttm drm_kms_helper drm i2c_algo_bit i2c_core
dm_mod [last unloaded: freq_table]
Pid: 13735, comm: srp_daemon Not tainted 2.6.32-71.el6.x86_64 #1
Call Trace:
[<ffffffff8106b857>] warn_slowpath_common+0x87/0xc0
[<ffffffff8106b8aa>] warn_slowpath_null+0x1a/0x20
[<ffffffff8125c39d>] kref_get+0x2d/0x30
[<ffffffffa01b4029>] rdac_bus_attach+0x459/0x580 [scsi_dh_rdac]
[<ffffffff8135232a>] scsi_dh_handler_attach+0x2a/0x80
[<ffffffff81352c7b>] scsi_dh_notifier+0x9b/0xa0
[<ffffffff814cd7a5>] notifier_call_chain+0x55/0x80
[<ffffffff8109711a>] __blocking_notifier_call_chain+0x5a/0x80
[<ffffffff81097156>] blocking_notifier_call_chain+0x16/0x20
[<ffffffff8132bec5>] device_add+0x515/0x640
[<ffffffff813329e4>] ? attribute_container_device_trigger+0xc4/0xe0
[<ffffffff8134f659>] scsi_sysfs_add_sdev+0x89/0x2c0
[<ffffffff8134d096>] scsi_probe_and_add_lun+0xea6/0xed0
[<ffffffff8134beb2>] ? scsi_alloc_target+0x292/0x2d0
[<ffffffff8134d1e1>] __scsi_scan_target+0x121/0x750
[<ffffffff811df806>] ? sysfs_create_file+0x26/0x30
[<ffffffff8132b759>] ? device_create_file+0x19/0x20
[<ffffffff81332838>] ? attribute_container_add_attrs+0x78/0x90
[<ffffffff814b008c>] ? klist_next+0x4c/0xf0
[<ffffffff81332e30>] ? transport_configure+0x0/0x20
[<ffffffff813329e4>] ? attribute_container_device_trigger+0xc4/0xe0
[<ffffffff8134df40>] scsi_scan_target+0xd0/0xe0
[<ffffffffa02f053a>] srp_create_target+0x75a/0x890 [ib_srp]
[<ffffffff8132a130>] dev_attr_store+0x20/0x30
[<ffffffff811df145>] sysfs_write_file+0xe5/0x170
[<ffffffff8116c818>] vfs_write+0xb8/0x1a0
[<ffffffff810d40a2>] ? audit_syscall_entry+0x272/0x2a0
[<ffffffff8116d251>] sys_write+0x51/0x90
[<ffffffff81013172>] system_call_fastpath+0x16/0x1b

Signed-off-by: Babu Moger <babu.moger@netapp.com>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/device_handler/scsi_dh_rdac.c

@@ -364,10 +364,7 @@ static void release_controller(struct kref *kref)
 	struct rdac_controller *ctlr;
 	ctlr = container_of(kref, struct rdac_controller, kref);
 
-	flush_workqueue(kmpath_rdacd);
-	spin_lock(&list_lock);
 	list_del(&ctlr->node);
-	spin_unlock(&list_lock);
 	kfree(ctlr);
 }
 
@@ -376,20 +373,17 @@ static struct rdac_controller *get_controller(int index, char *array_name,
 {
 	struct rdac_controller *ctlr, *tmp;
 
-	spin_lock(&list_lock);
-
 	list_for_each_entry(tmp, &ctlr_list, node) {
 		if ((memcmp(tmp->array_id, array_id, UNIQUE_ID_LEN) == 0) &&
 			  (tmp->index == index) &&
 			  (tmp->host == sdev->host)) {
 			kref_get(&tmp->kref);
-			spin_unlock(&list_lock);
 			return tmp;
 		}
 	}
 	ctlr = kmalloc(sizeof(*ctlr), GFP_ATOMIC);
 	if (!ctlr)
-		goto done;
+		return NULL;
 
 	/* initialize fields of controller */
 	memcpy(ctlr->array_id, array_id, UNIQUE_ID_LEN);
@@ -405,8 +399,7 @@ static struct rdac_controller *get_controller(int index, char *array_name,
 	INIT_WORK(&ctlr->ms_work, send_mode_select);
 	INIT_LIST_HEAD(&ctlr->ms_head);
 	list_add(&ctlr->node, &ctlr_list);
-done:
-	spin_unlock(&list_lock);
+
 	return ctlr;
 }
 
@@ -517,9 +510,12 @@ static int initialize_controller(struct scsi_device *sdev,
 			index = 0;
 		else
 			index = 1;
+
+		spin_lock(&list_lock);
 		h->ctlr = get_controller(index, array_name, array_id, sdev);
 		if (!h->ctlr)
 			err = SCSI_DH_RES_TEMP_UNAVAIL;
+		spin_unlock(&list_lock);
 	}
 	return err;
 }
@@ -906,7 +902,9 @@ static int rdac_bus_attach(struct scsi_device *sdev)
 	return 0;
 
 clean_ctlr:
+	spin_lock(&list_lock);
 	kref_put(&h->ctlr->kref, release_controller);
+	spin_unlock(&list_lock);
 
 failed:
 	kfree(scsi_dh_data);
@@ -921,14 +919,19 @@ static void rdac_bus_detach( struct scsi_device *sdev )
 	struct rdac_dh_data *h;
 	unsigned long flags;
 
-	spin_lock_irqsave(sdev->request_queue->queue_lock, flags);
 	scsi_dh_data = sdev->scsi_dh_data;
+	h = (struct rdac_dh_data *) scsi_dh_data->buf;
+	if (h->ctlr && h->ctlr->ms_queued)
+		flush_workqueue(kmpath_rdacd);
+
+	spin_lock_irqsave(sdev->request_queue->queue_lock, flags);
 	sdev->scsi_dh_data = NULL;
 	spin_unlock_irqrestore(sdev->request_queue->queue_lock, flags);
 
-	h = (struct rdac_dh_data *) scsi_dh_data->buf;
+	spin_lock(&list_lock);
 	if (h->ctlr)
 		kref_put(&h->ctlr->kref, release_controller);
+	spin_unlock(&list_lock);
 	kfree(scsi_dh_data);
 	module_put(THIS_MODULE);
 	sdev_printk(KERN_NOTICE, sdev, "%s: Detached\n", RDAC_NAME);