Hi,
After using logging in in "failsafe" mode, and using strace on kde, I
found out what was going on.
The following call now fails with ENOMEM:
mmap(NULL, 2147483648, PROT_READ|PROT_WRITE|PROT_EXEC,
MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE, -1, 0)
Older kernels did not enforce ulimit -d with MAP_NORESERVE (confirmed
this on (3.13.0-100-generic), whereas new ones do:
> uname -a ; ulimit -d 64000; ./memalloc-test 69000000
Linux lll 3.13.0-100-generic #147-Ubuntu SMP Tue Oct 18 16:48:51 UTC 2016
x86_64 x86_64 x86_64 GNU/Linux
Succeeded
> uname -a ; ulimit -d 64000; ./memalloc-test 69000000
Linux hitchhiker 4.7.0-0.bpo.1-amd64 #1 SMP Debian 4.7.8-1~bpo8+1 (2016-10-19)
x86_64 GNU/Linux
Malloc: Cannot allocate memory
I'm not sure where the bug actually is (kde or kernel), as indeed the
case could be made that KDE should not attempt to reserve a ridiculous
amount of memory if it never intends to use it (and it doesn't use it,
or else it would eventually get a SIGSEV on older kernels).
Thanks,
Alain
#include <stdlib.h>
#include <stdio.h>
#include <sys/mman.h>
int main(int argc, char **argv) {
void *r=mmap(0, atoi(argv[1]),
PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE,
-1,
0);
if(r != MAP_FAILED) {
printf("Succeeded\n");
} else {
perror("Malloc");
return -1;
}
return 0;
}
