Re: [PATCH -v4 1/8] locking/drm: Kill mutex trickery

[Peter Zijlstra]

On Sat, Oct 08, 2016 at 01:58:07PM +0200, Thomas Gleixner wrote:
> Hmm. I'm not a great fan of this, because that requires an conditional
> unlock mechanism.
> 
>        res = trylock_recursive(lock);
>        if (res == FAILED)
>        	       goto out;
>        .....
> 
>        if (res == SUCCESS)
>        	       unlock(lock);
> 
> While if you actually keep track of recursion you can do:
>   
>       if (!trylock_recursive(lock))
> 		goto out;
> 
>       ....
> 
>       unlock_recursive(lock);
> 
> or even:
> 
>      lock_recursive(lock);
> 
>      unlock_recursive(lock);
> 
> That's making lock/trylock and unlock symetric, so its obvious in the
> source what's going on and the recursion tracking allows for better
> debugability.

Hurm,. so I thought that in general we disliked recursive locking
because it quickly turns in to a horrible mess.

Adding such primitives makes it 'easy' to use recursive locking and then
where does it stop?