vm: fix a null dereference on out-of-memory

. also make other out-of-memory conditions less fatal
	. add a test case for a user program using all the memory
	  it can
	. remove some diagnostic prints for situations that are normal
	  when running out of memory so running the test isn't noisy

test/Makefile

@@ -23,7 +23,7 @@ OBJS.test57=test57loop.o
  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 \
 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 \
 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 \
-61 62
+61 62 64
 PROG+= test$(t)
 .endfor
   

test/run

@@ -14,7 +14,7 @@ badones=			# list of tests that failed
 tests="   1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 \
          21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 \
          41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 \
-         61 62 63 \
+         61 62 63 64 \
 	 sh1.sh sh2.sh interp.sh"
 tests_no=`expr 0`
 

test/test64.c

@@ -0,0 +1,48 @@
+
+/* Code to test reasonable response to out-of-memory condition
+ * of regular processes.
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <dlfcn.h>
+
+#include <sys/mman.h>
+#include <sys/wait.h>
+
+#define MAX_ERROR 2
+
+#include "magic.h"
+#include "common.c"
+
+int main (int argc, char *argv[])
+{
+  pid_t f;
+  start(64);
+#define NADDRS 500
+#define LEN 4096
+  static void *addrs[NADDRS];
+  int i = 0;
+  int st;
+
+  if((f=fork()) == -1) {
+  	e(1);
+	exit(1);
+  }
+
+  if(f == 0) {
+  	/* child: use up as much memory as we can */
+	while((addrs[i++ % NADDRS] = minix_mmap(0, LEN, PROT_READ|PROT_WRITE,
+		MAP_PREALLOC|MAP_CONTIG|MAP_ANON, -1, 0)) != MAP_FAILED)
+			;
+	exit(0);
+  }
+
+  /* parent: wait for child */
+  if(waitpid(f, &st, 0) < 0) 
+	perror("waitpid");
+
+  quit();
+
+  return(0);
+}