md: add comments in md_integrity_register

Given it is not obvious for the error handling, let's try to add some
comments here to make it clear.
Signed-off-by: Guoqing Jiang <jiangguoqing@kylinos.cn>
Signed-off-by: Song Liu <song@kernel.org>

drivers/md/md.c

@@ -2343,6 +2343,12 @@ int md_integrity_register(struct mddev *mddev)
 	if (bioset_integrity_create(&mddev->bio_set, BIO_POOL_SIZE) ||
 	    (mddev->level != 1 && mddev->level != 10 &&
 	     bioset_integrity_create(&mddev->io_acct_set, BIO_POOL_SIZE))) {
+		/*
+		 * No need to handle the failure of bioset_integrity_create,
+		 * because the function is called by md_run() -> pers->run(),
+		 * md_run calls bioset_exit -> bioset_integrity_free in case
+		 * of failure case.
+		 */
 		pr_err("md: failed to create integrity pool for %s\n",
 		       mdname(mddev));
 		return -EINVAL;