diff --git a/sys/kern/kern_ktrace.c b/sys/kern/kern_ktrace.c
index 5ad5272af7d8..787e44d6b3a3 100644
--- a/sys/kern/kern_ktrace.c
+++ b/sys/kern/kern_ktrace.c
@@ -1281,8 +1281,10 @@ ktrwrite(struct ktr_desc *ktd, struct ktrace_entry *kte)
 	struct ktrace_entry *top = kte;
 	struct ktr_header *kth;
 	file_t *fp = ktd->ktd_fp;
+	unsigned loopcount, zzzcount;
 	int error;
 next:
+	loopcount = zzzcount = 0;
 	auio.uio_iov = iov = &aiov[0];
 	auio.uio_offset = 0;
 	auio.uio_rw = UIO_WRITE;
@@ -1330,19 +1332,40 @@ next:
 	    auio.uio_iovcnt < sizeof(aiov) / sizeof(aiov[0]) - 1);
 
 again:
+    {
+	size_t resid = auio.uio_resid;
+	int i;
+
+	for (i = 0; i < auio.uio_iovcnt; i++) {
+		KASSERTMSG(auio.uio_iov[i].iov_len <= resid,
+		    "uio_iov[%u].iov_len=%zu > resid=%zu;"
+		    " total=%zu loopcount=%u zzzcount=%u",
+		    i, auio.uio_iov[i].iov_len, resid,
+		    auio.uio_resid, loopcount, zzzcount);
+		resid -= auio.uio_iov[i].iov_len;
+	}
+	KASSERTMSG(resid == 0, "iovcnt=%d resid=%zu;"
+	    " total=%zu loopcount=%u zzzcount=%u",
+	    auio.uio_iovcnt, resid,
+	    auio.uio_resid, loopcount, zzzcount);
+    }
+
 	error = (*fp->f_ops->fo_write)(fp, &fp->f_offset, &auio,
 	    fp->f_cred, FOF_UPDATE_OFFSET);
 	switch (error) {
 
 	case 0:
-		if (auio.uio_resid > 0)
+		if (auio.uio_resid > 0) {
+			loopcount++;
 			goto again;
+		}
 		if (kte != NULL)
 			goto next;
 		break;
 
 	case EWOULDBLOCK:
 		kpause("ktrzzz", false, 1, NULL);
+		zzzcount++;
 		goto again;
 
 	default:
diff --git a/sys/kern/subr_copy.c b/sys/kern/subr_copy.c
index cd934032d33c..15e2c4a73e18 100644
--- a/sys/kern/subr_copy.c
+++ b/sys/kern/subr_copy.c
@@ -110,6 +110,21 @@ uiomove(void *buf, size_t n, struct uio *uio)
 
 	ASSERT_SLEEPABLE();
 
+    {
+	size_t resid = uio->uio_resid;
+	int i;
+
+	for (i = 0; i < uio->uio_iovcnt; i++) {
+		KASSERTMSG(uio->uio_iov[i].iov_len <= resid,
+		    "uio_iov[%u].iov_len=%zu > resid=%zu;"
+		    " total=%zu n=%zu",
+		    i, uio->uio_iov[i].iov_len, resid, uio->uio_resid, n);
+		resid -= uio->uio_iov[i].iov_len;
+	}
+	KASSERTMSG(resid == 0, "iovcnt=%d resid=%zu; total=%zu n=%zu",
+	    uio->uio_iovcnt, resid, uio->uio_resid, n);
+    }
+
 	KASSERT(uio->uio_rw == UIO_READ || uio->uio_rw == UIO_WRITE);
 	while (n > 0 && uio->uio_resid) {
 		KASSERT(uio->uio_iovcnt > 0);