Created attachment 6511 [details]
The Patch can fix the race betweent atexit() and exit()

exit() uses global variable __exit_funcs indirectly, which are not protected.
It is not safe in multithread circumstance.

When call exit() and atexit() simultaneously in multithread circumstance,
the following case will cause unsafe.
The case has main process A and thread B.

a. thread B call atexit()
b. process A call exit() to traverse the __exit_funcs list
c. thread B call calloc() to create a new entry p, and next to listp:
   p->next = *listp;
d. process A modify listp to cur's next, then free cur:
   *listp = cur->next;
e. thread B modify listp to p:
   *listp = p;
f. when get f, the f is undefined:
   const struct exit_function *const f =
     &cur->fns[--cur->idx];
g. programme may be Segmentation fault