Re: [PATCH] [RFC] Fix pthread timeout handling and cancellation issues

[Richard Braun]

On Thu, Jan 24, 2013 at 12:14:44AM +0100, Richard Braun wrote:
> diff --git a/pthread/pt-cancel.c b/pthread/pt-cancel.c
> index d19c557..3698cce 100644
> --- a/pthread/pt-cancel.c
> +++ b/pthread/pt-cancel.c
> @@ -31,9 +31,31 @@ pthread_cancel (pthread_t t)
>    if (! p)
>      return ESRCH;
>  
> +  __pthread_mutex_lock (&p->cancel_lock);
> +  if (p->cancel_pending)
> +    {
> +      __pthread_mutex_unlock (&p->cancel_lock);
> +      return 0;
> +    }
> +
>    p->cancel_pending = 1;
> -  if (p->cancel_state == PTHREAD_CANCEL_ENABLE
> -      && p->cancel_type == PTHREAD_CANCEL_ASYNCHRONOUS)
> +
> +  if (p->cancel_state != PTHREAD_CANCEL_ENABLE)
> +    {
> +      __pthread_mutex_unlock (&p->cancel_lock);
> +      return 0;
> +    }
> +
> +  /* Thread blocking on a cancellation point.  Invoke hook to unblock.
> +     See __pthread_cond_timedwait_internal.  */
> +  if (p->cancel_hook != NULL)
> +    {
> +      assert (p->cancel_type == PTHREAD_CANCEL_DEFERRED);
> +      p->cancel_hook (p->cancel_hook_arg);
> +      __pthread_mutex_unlock (&p->cancel_lock);
> +    }
> +  else if (p->cancel_type == PTHREAD_CANCEL_ASYNCHRONOUS)
> +    /* CANCEL_LOCK is unlocked by this call.  */
>      err = __pthread_do_cancel (p);

There is an obvious locking issue here where pthread_cancel could return
while the cancel lock hasn't been released. Consider it fixed.

-- 
Richard Braun