Re: [Xenomai-core] [Xenomai-help] What have I misunderstood about condition variables

[Philippe Gerum <rpm@xenomai.org>]

Anders Blomdell wrote:
> OK, found the bug (not mine!).

No, it's mine. Actually, you fixed two of them, since nested locks would not be
released properly when entering cond_wait. Will merge, thanks.

 I suggest something like this:
> 
> --- ksrc/skins/native/cond.c.orig       2008-03-11 20:42:52.000000000 +0100
> +++ ksrc/skins/native/cond.c    2008-03-11 21:00:10.000000000 +0100
> @@ -438,13 +438,20 @@
> 
>  int rt_cond_wait(RT_COND *cond, RT_MUTEX *mutex, RTIME timeout)
>  {
> -       int err, kicked = 0;
> +       /* We can't use rt_mutex_release since that might reschedule
> +          before we do our xnsynch_sleep_on, hence most of of the code
> +          is duplicated here */
> +       int err = 0, kicked = 0;
>         xnthread_t *thread;
>         spl_t s;
> +       int lockcnt;
> 
>         if (timeout == TM_NONBLOCK)
>                 return -EWOULDBLOCK;
> 
> +       if (xnpod_unblockable_p())
> +               return -EPERM;
> +
>         xnlock_get_irqsave(&nklock, s);
> 
>         cond = xeno_h2obj_validate(cond, XENO_COND_MAGIC, RT_COND);
> @@ -454,10 +461,26 @@
>                 goto unlock_and_exit;
>         }
> 
> -       err = rt_mutex_release(mutex);
> +       mutex = xeno_h2obj_validate(mutex, XENO_MUTEX_MAGIC, RT_MUTEX);
> 
> -       if (err)
> +       if (!mutex) {
> +               err = xeno_handle_error(mutex, XENO_MUTEX_MAGIC, RT_MUTEX);
> +               goto unlock_and_exit;
> +       }
> +
> +       if (xnpod_current_thread() != xnsynch_owner(&mutex->synch_base)) {
> +               err = -EPERM;
>                 goto unlock_and_exit;
> +       }
> +
> +       lockcnt = mutex->lockcnt; /* Leave even if mutex is nested */
> +
> +       mutex->lockcnt = 0;
> +
> +       if (xnsynch_wakeup_one_sleeper(&mutex->synch_base)) {
> +               mutex->lockcnt = 1;
> +               /* Scheduling deferred */
> +       }
> 
>         thread = xnpod_current_thread();
> 
> @@ -474,6 +497,8 @@
> 
>         rt_mutex_acquire(mutex, TM_INFINITE);
> 
> +       mutex->lockcnt = lockcnt; /* Adjust lockcnt */
> +
>         if (kicked)
>                 xnthread_set_info(thread, XNKICKED);
> 
> 
> 
> 


-- 
Philippe.