The cure is a simple patch in libc-5.2.18 which follows.
BTW, I noticed that I could not compile libc-5.2.18 using the includes
from kernel 1.3.68, but it did compile with the includes from Slackware
3.0's 1.2.13 elf-patched kernel sources.
--- libc/sysdeps/linux/i386/getprio.c.orig Sat Feb 18 07:33:34 1995
+++ libc/sysdeps/linux/i386/getprio.c Mon Feb 26 16:37:15 1996
@@ -2,7 +2,7 @@
#include <sys/resource.h>
#include <sys/syscall.h>
-#define PZERO 15
+#define PZERO 20
int
getpriority(int which, int who)