From e1a37303c89696a110c61a156768ea15cc03a246 Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Fri, 20 Sep 2019 12:13:57 -0400
Subject: yet another sbrk() bug fix, and usertest
---
user/usertests.c | 25 ++++++++++++++++++++++---
1 file changed, 22 insertions(+), 3 deletions(-)
(limited to 'user')
diff --git a/user/usertests.c b/user/usertests.c
index 0f4a443..608cd3f 100644
--- a/user/usertests.c
+++ b/user/usertests.c
@@ -1924,9 +1924,10 @@ pgbug(char *s)
}
// does the kernel panic if a process sbrk()s its size to be less than
-// a page, or zero?
+// a page, or zero, or reduces the break by an amount too small to
+// cause a page to be freed?
void
-zerosize(char *s)
+sbrkbugs(char *s)
{
int pid = fork();
if(pid < 0){
@@ -1959,6 +1960,24 @@ zerosize(char *s)
}
wait(0);
+ pid = fork();
+ if(pid < 0){
+ printf("fork failed\n");
+ exit(1);
+ }
+ if(pid == 0){
+ // set the break in the middle of a page.
+ sbrk((10*4096 + 2048) - (uint64)sbrk(0));
+
+ // reduce the break a bit, but not enough to
+ // cause a page to be freed. this used to cause
+ // a panic.
+ sbrk(-10);
+
+ exit(0);
+ }
+ wait(0);
+
exit(0);
}
@@ -2000,7 +2019,7 @@ main(int argc, char *argv[])
char *s;
} tests[] = {
{pgbug, "pgbug" },
- {zerosize, "zerosize" },
+ {sbrkbugs, "sbrkbugs" },
{reparent, "reparent" },
{twochildren, "twochildren"},
{forkfork, "forkfork"},
--
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