Comment 20 for bug 425723

Created attachment 4001
deadlock-free proposed patch

Revised patch; unfortunately, the ATOMIC_FASTBINS stuff makes the code fairly
ugly now... getting rid of the #if 0 bit might help a little.

Without this patch, this crashes in few tens of seconds on my four-core when
run with MALLOC_CHECK_=3:

/* compile with -fopenmp */
#include <stdlib.h>
#include <unistd.h>

int main(void)
{
#pragma omp parallel num_threads(256)
  while (1) {
    void *ptr = malloc(rand() % 65536);
    usleep((rand() % 100) * 100);
    free(ptr);
    usleep((rand() % 100) * 100);
  }
  return 0;
}