scsi: core: Simplify LLD module reference counting

Swap two statements in scsi_device_put() now that it is guaranteed that
SCSI hosts outlive SCSI devices. Remove the reference counting code from
scsi_sysfs.c that became superfluous because SCSI hosts now outlive SCSI
devices.

Link: https://lore.kernel.org/r/20220728221851.1822295-4-bvanassche@acm.org
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Mike Christie <michael.christie@oracle.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: John Garry <john.garry@huawei.com>
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
[ bvanassche: Extracted this patch from a larger patch ]
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi.c

@@ -586,10 +586,13 @@ EXPORT_SYMBOL(scsi_device_get);
  */
 void scsi_device_put(struct scsi_device *sdev)
 {
-	struct module *mod = sdev->host->hostt->module;
-
+	/*
+	 * Decreasing the module reference count before the device reference
+	 * count is safe since scsi_remove_host() only returns after all
+	 * devices have been removed.
+	 */
+	module_put(sdev->host->hostt->module);
 	put_device(&sdev->sdev_gendev);
-	module_put(mod);
 }
 EXPORT_SYMBOL(scsi_device_put);
 

drivers/scsi/scsi_sysfs.c

@@ -452,9 +452,6 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
 	struct scsi_vpd *vpd_pg0 = NULL, *vpd_pg89 = NULL;
 	struct scsi_vpd *vpd_pgb0 = NULL, *vpd_pgb1 = NULL, *vpd_pgb2 = NULL;
 	unsigned long flags;
-	struct module *mod;
-
-	mod = sdev->host->hostt->module;
 
 	scsi_dh_release_device(sdev);
 
@@ -521,17 +518,11 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
 
 	if (parent)
 		put_device(parent);
-	module_put(mod);
 }
 
 static void scsi_device_dev_release(struct device *dev)
 {
 	struct scsi_device *sdp = to_scsi_device(dev);
-
-	/* Set module pointer as NULL in case of module unloading */
-	if (!try_module_get(sdp->host->hostt->module))
-		sdp->host->hostt->module = NULL;
-
 	execute_in_process_context(scsi_device_dev_release_usercontext,
 				   &sdp->ew);
 }