[PATCH] newlib: Unlock the mutex while calling atexit()'ed functions

[Corinna Vinschen]

Hi Takashi,

On Nov 18 22:31, Takashi Yano wrote:
> The atexit()'ed function may deadlock if it waits for another thread
> which calls atexit() in the current __call_atexit.c code. This patch
> unlock __atexit_recursive_mutex while calling atexit()'ed functions
> to avoid the deadlock mentioned above. glibc and Darwin do the same,
> so it sounds reasonable.
> 
> Addresses: https://cygwin.com/pipermail/cygwin/2025-October/258930.html
> Reported-by: Tomohiro Kashiwada <tomohiro-kashiwada@ezweb.ne.jp>
> Reviewed-by:
> Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
> ---
>  newlib/libc/stdlib/__call_atexit.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/newlib/libc/stdlib/__call_atexit.c b/newlib/libc/stdlib/__call_atexit.c
> index 710440389..44f1f6acc 100644
> --- a/newlib/libc/stdlib/__call_atexit.c
> +++ b/newlib/libc/stdlib/__call_atexit.c
> @@ -114,6 +114,11 @@ __call_exitprocs (int code, void *d)
>  
>  	  ind = p->_ind;
>  
> +#ifndef __SINGLE_THREAD__
> +	  /* Unlock __atexit_recursive_mutex; otherwise, the function fn() may
> +	     deadlock if it waits for another thread which calls atexit(). */
> +	  __lock_release_recursive(__atexit_recursive_mutex);
> +#endif
>  	  /* Call the function.  */
>  	  if (!args || (args->_fntypes & i) == 0)
>  	    fn ();
> @@ -121,6 +126,9 @@ __call_exitprocs (int code, void *d)
>  	    (*((void (*)(int, void *)) fn))(code, args->_fnargs[n]);
>  	  else
>  	    (*((void (*)(void *)) fn))(args->_fnargs[n]);
> +#ifndef __SINGLE_THREAD__
> +	  __lock_acquire_recursive(__atexit_recursive_mutex);
> +#endif
>  
>  	  /* The function we called call atexit and registered another
>  	     function (or functions).  Call these new functions before
> -- 
> 2.51.0

LGTM, please push.


Thanks,
Corinna