Index: sys/dev/random/randomdev.c
===================================================================
--- sys/dev/random/randomdev.c
+++ sys/dev/random/randomdev.c
@@ -130,6 +130,8 @@
 	uint8_t *random_buf;
 	int error, spamcount;
 	ssize_t read_len, total_read, c;
+	/* 16 MiB takes about 0.08 s CPU time on my 2017 AMD Zen CPU */
+	const size_t sigchk_period = 16 * 1024 * 1024;
 
 	random_buf = malloc(PAGE_SIZE, M_ENTROPY, M_WAITOK);
 	p_random_alg_context->ra_pre_read();
@@ -167,12 +169,26 @@
 			read_len = MIN(read_len, PAGE_SIZE);
 			p_random_alg_context->ra_read(random_buf, read_len);
 			c = MIN(uio->uio_resid, read_len);
+			/*
+			 * uiomove() may yield the CPU before each 'c' bytes
+			 * (up to PAGE_SIZE) are copied out.
+			 */
 			error = uiomove(random_buf, c, uio);
 			total_read += c;
+			/*
+			 * Poll for signals every few MBs to avoid very long
+			 * uninterruptible syscalls.
+			 */
+			if (error == 0 && uio->uio_resid != 0 &&
+			    (total_read - c) / sigchk_period !=
+			    total_read / sigchk_period)
+				error = tsleep_sbt(&random_alg_context, PCATCH,
+				    "randrd", SBT_1NS, 0, C_HARDCLOCK);
 		}
-		if (total_read != uio->uio_resid && (error == ERESTART || error == EINTR))
+		if (error == ERESTART || error == EINTR) {
 			/* Return partial read, not error. */
 			error = 0;
+		}
 	}
 	free(random_buf, M_ENTROPY);
 	return (error);