Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1497754

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

Show all headers | View raw

On Sat, 8 Oct 2016, Peter Zijlstra wrote:
> 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?

Well, when you add just trylock_recursive then people are going to use it
anyway no matter whether it is easy or not.

So if we decide to provide something which supports recursive locking for
mutexes then we are better off doing it with a proper set of functions and
not just a single undebugable wrapper.

Thanks,

	tglx

 

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[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

csiph-web