[PATCH v3] dlfcn: Fix dlclose crash in atexit handler after thread_local destructor (BZ 33598)

[Florian Weimer]

* Adhemerval Zanella:

> @@ -46,6 +47,9 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
>    /* The exit should never return, so there is no need to unlock it.  */
>    __libc_lock_lock_recursive (__exit_lock);
>  
> +  /* Disable unmap objects through dlclose by TLS destructor (BZ 33598).  */
> +  GL(dl_at_exit) = true;
> +
>    /* First, call the TLS destructors.  */
>    if (run_dtors)
>      call_function_static_weak (__call_tls_dtors);
> diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
> index 15c46598539..236419c593c 100644
> --- a/sysdeps/generic/ldsodefs.h
> +++ b/sysdeps/generic/ldsodefs.h
> @@ -441,6 +441,9 @@ struct rtld_global
>    /* Generation counter for the dtv.  */
>    EXTERN size_t _dl_tls_generation;
>  
> +  /* Disable unmap objects during __run_exit_handlers.  */
> +  EXTERN bool _dl_at_exit;
> +
>    /* Scopes to free after next THREAD_GSCOPE_WAIT ().  */
>    EXTERN struct dl_scope_free_list
>    {

Would it be simpler to do what the comment says?  Just guard the
munmap call that is part of dlclose?  This could even be considered an
optimization.