[PATCH v2 1/1] scsi: Fix racing between dev init and dev reset

[Alice Chao <alice.chao@mediatek.com>]

Device reset thread uses kobject_uevent_env() to get kobj.parent
after scsi_evt_emit(), and it races with device init thread which
calls device_add() to create kobj.parent before kobject_uevent_env().

Device reset call trace:
fill_kobj_path
kobject_get_path
kobject_uevent_env
scsi_evt_emit			<- add wait_event()
scsi_evt_thread

Device init call trace:
fill_kobj_path
kobject_get_path
kobject_uevent_env
device_add				<- create kobj.parent
scsi_target_add
scsi_sysfs_add_sdev
scsi_add_lun
scsi_probe_and_add_lun

These two jobs are scheduled asynchronously, we can't guaranteed that
kobj.parent will be created in device init thread before device reset
thread calls kobj_get_path().

To resolve the racing issue between device init thread and device
reset thread, we use wait_event() in scsi_evt_emit() to wait for
device_add() to complete the creation of kobj.parent.

Signed-off-by: Alice Chao <alice.chao@mediatek.com>
---
 drivers/scsi/scsi_lib.c  | 1 +
 drivers/scsi/scsi_scan.c | 1 +
 2 files changed, 2 insertions(+)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 0a70aa763a96..abf9a71ed77c 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2461,6 +2461,7 @@ static void scsi_evt_emit(struct scsi_device *sdev, struct scsi_event *evt)
 		break;
 	case SDEV_EVT_POWER_ON_RESET_OCCURRED:
 		envp[idx++] = "SDEV_UA=POWER_ON_RESET_OCCURRED";
+		wait_event(sdev->host->host_wait, sdev->sdev_gendev.kobj.parent != NULL);
 		break;
 	default:
 		/* do nothing */
diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index f4e6c68ac99e..431f229ac435 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -1904,6 +1904,7 @@ static void do_scsi_scan_host(struct Scsi_Host *shost)
 	} else {
 		scsi_scan_host_selected(shost, SCAN_WILD_CARD, SCAN_WILD_CARD,
 				SCAN_WILD_CARD, 0);
+		wake_up(&shost->host_wait);
 	}
 }
 
-- 
2.18.0