On 25 April 2012 01:10, Siddhesh Poyarekar <siddhesh.poyarekar@xxxxxxxxx> wrote:
> That was supposed to be errno, not the pointer. I had added my own
> syscall wrappers to eliminate glibc and then reverted it to the
> original smaller-to-read reproducer and this got left behind in the
> process. The demo program is supposed to show "successed" for
> iterations 16383 to 16390 since the overflow happens at 16TB. All
> iterations before it (and after) show a fork failure.
>
> /proc/sys/vm/overcommit_memory is 0.
>
> Perhaps a cleaner demo program would have been:
Ugh, I missed some details once again. The demo below will show
"Unexpected success" without this patch in place. The system I've
tested this patch on is an x86_64 F-16 box with 4GB RAM and 6GB swap.
> #include <stdio.h>
> #include <unistd.h>
> #include <sys/mman.h>
> #include <errno.h>
>
> #define GIG 1024 * 1024 * 1024L
> #define EXTENT 16393
>
> int main(void)
> {
> int i, r;
> void *m;
> char buf[1024];
> int prev_failed = 0;
>
> for (i = 0; i < EXTENT; i++) {
> m = mmap(NULL, (size_t) 1 * 1024 * 1024 * 1024L,
> PROT_READ | PROT_WRITE, MAP_PRIVATE |
> MAP_ANONYMOUS, 0, 0);
>
> if (m == (void *)-1) {
> printf("MMAP Failed: %d\n", errno);
> return 1;
> }
>
> r = fork();
>
> if (r == 0) {
> return 0;
> } else if (r < 0) {
> prev_failed = 1;
> /* Fork failed as expected */
> }
> else if (r > 0 && prev_failed) {
> printf("Unexpected success at %d\n", i);
> wait(NULL);
> return 1;
> }
> }
> return 0;
> }
>
--
Siddhesh Poyarekar
http://siddhesh.in
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