Re: hugetlb: reservation race leading to under provisioning

[Michal Hocko <mhocko@kernel.org>]

I have only now realized I haven't attached the promissed program to
replicate the issue.

$ cat badmmap.c
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <hugetlbfs.h>
#include <sys/mman.h>
int main(int argc, const char **argv) {
  const size_t len = 224 * 1024 * 1024;
  int count = (argc > 1) ? atoi(argv[1]) : 1000;
  int i;
  for (i = 0; i < count; ++i) {
    int fd = hugetlbfs_unlinked_fd();
    void *ptr = mmap(0, len, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
    if (ptr == MAP_FAILED) {
      fprintf(stderr, "mmap() failed on iteration %d (%s)\n", i, strerror(errno));
      return 1;
    }
    close(fd);
    if (munmap(ptr, len) < 0) {
      fprintf(stderr, "munmap() failed on iteration %d (%s)\n", i, strerror(errno));
      return 1;
    }
  }
  printf("PASSED %d iters\n", count);
  return 0;
}

$ cc -o badmmap badmmap.c -lhugetlbfs

Run 8 or so instances in parallel to reproduce.
-- 
Michal Hocko
SUSE Labs

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