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

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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?

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[PATCH -v4 0/8] locking/mutex: Rewrite basic mutex Peter Zijlstra <peterz@infradead.org> - 2016-10-07 17:10 +0200
  [PATCH -v4 4/8] locking/mutex: Allow MUTEX_SPIN_ON_OWNER when DEBUG_MUTEXES Peter Zijlstra <peterz@infradead.org> - 2016-10-07 17:10 +0200
  [PATCH -v4 7/8] locking/mutex: Simplify some ww_mutex code in __mutex_lock_common() Peter Zijlstra <peterz@infradead.org> - 2016-10-07 17:10 +0200
  [PATCH -v4 6/8] locking/mutex: Restructure wait loop Peter Zijlstra <peterz@infradead.org> - 2016-10-07 17:30 +0200
  [PATCH -v4 8/8] locking/mutex: Enable optimistic spinning of woken waiter Peter Zijlstra <peterz@infradead.org> - 2016-10-07 17:30 +0200
  [PATCH -v4 2/8] locking/mutex: Rework mutex::owner Peter Zijlstra <peterz@infradead.org> - 2016-10-07 17:30 +0200
    Re: [PATCH -v4 2/8] locking/mutex: Rework mutex::owner Davidlohr Bueso <dave@stgolabs.net> - 2016-10-12 20:40 +0200
      Re: [PATCH -v4 2/8] locking/mutex: Rework mutex::owner Jason Low <jason.low2@hpe.com> - 2016-10-12 22:00 +0200
  [PATCH -v4 5/8] locking/mutex: Add lock handoff to avoid starvation Peter Zijlstra <peterz@infradead.org> - 2016-10-07 17:40 +0200
  [PATCH -v4 1/8] locking/drm: Kill mutex trickery Peter Zijlstra <peterz@infradead.org> - 2016-10-07 17:40 +0200
    Re: [PATCH -v4 1/8] locking/drm: Kill mutex trickery Peter Zijlstra <peterz@infradead.org> - 2016-10-07 17:50 +0200
      Re: [PATCH -v4 1/8] locking/drm: Kill mutex trickery Linus Torvalds <torvalds@linux-foundation.org> - 2016-10-07 18:00 +0200
        Re: [PATCH -v4 1/8] locking/drm: Kill mutex trickery Peter Zijlstra <peterz@infradead.org> - 2016-10-07 18:20 +0200
      Re: [PATCH -v4 1/8] locking/drm: Kill mutex trickery Thomas Gleixner <tglx@linutronix.de> - 2016-10-08 14:10 +0200
        Re: [PATCH -v4 1/8] locking/drm: Kill mutex trickery Thomas Gleixner <tglx@linutronix.de> - 2016-10-08 16:20 +0200
          Re: [PATCH -v4 1/8] locking/drm: Kill mutex trickery Peter Zijlstra <peterz@infradead.org> - 2016-10-08 18:50 +0200
        Re: [PATCH -v4 1/8] locking/drm: Kill mutex trickery Peter Zijlstra <peterz@infradead.org> - 2016-10-08 16:20 +0200
  [PATCH -v4 3/8] locking/mutex: Kill arch specific code Peter Zijlstra <peterz@infradead.org> - 2016-10-07 17:40 +0200
  Re: [PATCH -v4 0/8] locking/mutex: Rewrite basic mutex Linus Torvalds <torvalds@linux-foundation.org> - 2016-10-07 17:50 +0200
  Re: [PATCH -v4 0/8] locking/mutex: Rewrite basic mutex Jason Low <jason.low2@hpe.com> - 2016-10-11 21:10 +0200

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