Re: Recursion bug in -rt

[David Singleton <dsingleton@mvista.com>]

Dinakar Guniguntala wrote:

Dinakar,
   the new patch is available at

    http://source.mvista.com/~dsingleton/patch-2.6.15-rc5-rt2-rf4

thanks for the patch and the testing.

David


> On Fri, Dec 16, 2005 at 01:26:44PM -0800, David Singleton wrote:
>  
>
> > Dinakar,
> >
> >    I believe this patch will give you the behavior you expect.
> >
> >   http://source.mvista.com/~dsingleton/patch-2.6.15-rc5-rt2-rf3
> >    
>
> Not really, the reason, quoting from my previous mail
>
>   So IMO the above check is not right. However removing this check
>   is not the end of story.  This time it gets to task_blocks_on_lock
>   and tries to grab the task->pi_lock of the owvner which is itself
>   and results in a system hang. (Assuming CONFIG_DEBUG_DEADLOCKS
>   is not set). So it looks like we need to add some check to
>   prevent this below in case lock_owner happens to be current.
>
>    _raw_spin_lock(&lock_owner(lock)->task->pi_lock);
>
> The patch that works for me is attached below
>
> 	-Dinakar
>
>
>  
>
> ------------------------------------------------------------------------
>
> Index: linux-2.6.14-rt22-rayrt5/kernel/rt.c
> ===================================================================
> --- linux-2.6.14-rt22-rayrt5.orig/kernel/rt.c	2005-12-15 02:15:13.000000000 +0530
> +++ linux-2.6.14-rt22-rayrt5/kernel/rt.c	2005-12-19 15:51:26.000000000 +0530
> @@ -1042,7 +1042,8 @@
> 		return;
> 	}
> #endif
> -	_raw_spin_lock(&lock_owner(lock)->task->pi_lock);
> +	if (current != lock_owner(lock)->task)
> +		_raw_spin_lock(&lock_owner(lock)->task->pi_lock);
> 	plist_add(&waiter->pi_list, &lock_owner(lock)->task->pi_waiters);
> 	/*
> 	 * Add RT tasks to the head:
> @@ -1055,7 +1056,8 @@
> 	 */
> 	if (task->prio < lock_owner(lock)->task->prio)
> 		pi_setprio(lock, lock_owner(lock)->task, task->prio);
> -	_raw_spin_unlock(&lock_owner(lock)->task->pi_lock);
> +	if (current != lock_owner(lock)->task)
> +		_raw_spin_unlock(&lock_owner(lock)->task->pi_lock);
> }
>
> /*
> @@ -3016,8 +3018,7 @@
> 	 * the first waiter and we'll just block on the down_interruptible.
> 	 */
>
> -	if (owner_task != current)
> -		down_try_futex(lock, owner_task->thread_info __EIP__);
> +	down_try_futex(lock, owner_task->thread_info __EIP__);
>
> 	/*
> 	 * we can now drop the locks because the rt_mutex is held.
>  

-
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