nbd: Use invalidate_disk() helper on disconnect

When a nbd device encounters a writeback error, that error will
get propagated to the bd_inode's wb_err field. Then if this nbd
device's backend is disconnected and another is attached, we will
get back the previous writeback error on fsync, which is unexpected.

To fix it, let's use invalidate_disk() helper to invalidate the
disk on disconnect instead of just setting disk's capacity to zero.

Signed-off-by: Xie Yongji <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jens Axboe <[e-mail]>

drivers/block/nbd.c

···
 	nsock->sent = 0;
 }
 
-static void nbd_size_clear(struct nbd_device *nbd)
-{
-	if (nbd->config->bytesize) {
-		set_capacity(nbd->disk, 0);
-		kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
-	}
-}
-
 static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize,
 		loff_t blksize)
 {
···
 					&nbd->config_lock)) {
 		struct nbd_config *config = nbd->config;
 		nbd_dev_dbg_close(nbd);
-		nbd_size_clear(nbd);
+		invalidate_disk(nbd->disk);
+		if (nbd->config->bytesize)
+			kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
 		if (test_and_clear_bit(NBD_RT_HAS_PID_FILE,
 				       &config->runtime_flags))
 			device_remove_file(disk_to_dev(nbd->disk), &pid_attr);