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Re: [PATCH] mutex: make mutex_lock_nested an inline function

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On Wed, Oct 14, 2015 at 11:27:06AM +0100, Mark Brown wrote:
> On Wed, Oct 14, 2015 at 10:20:50AM +0200, Peter Zijlstra wrote:
> 
> > Uuh, I just looked at next and saw this regulator_lock_supply()
> > function. How is that limited? subclass must be <8 otherwise bad things
> > happen.
> 
> Can we please get some more discoverable documentation of the arbitrary
> limits in the lockdep code? 

include/linux/lockdep.h:#define MAX_LOCKDEP_SUBCLASSES          8UL

Also, it will give a runtime warn if you ever do hit that.

> I seem to keep seeing code that bumps into
> surprising limits like this and I'm not sure how I'm supposed to know
> about them except through finding out after the fact or trawling the
> code every time someone touches locking.

Not knowing what other limits you've hit, I'm not entirely sure how to
help out there.

> I would be very surprised to see a system that pushes over 8 locks,
> while there's nothing actually preventing it system design
> considerations mean that even four cascaded supplies are pretty
> unlikely so we should be fine.  Every time you add a new level of
> regulation you're both increasing the load on regulators up the chain
> (which means they need to be bigger and more expensive) and except in
> the case of a DCDC supplying an LDO (which only works to one level)
> you're going to be decreasing the efficiency of the system.  If we get
> to that point we can worry about what to do.

OK I suppose.
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Re: [PATCH] mutex: make mutex_lock_nested an inline function Peter Zijlstra <peterz@infradead.org> - 2015-10-13 22:40 +0200
  Re: [PATCH] mutex: make mutex_lock_nested an inline function Arnd Bergmann <arnd@arndb.de> - 2015-10-13 23:50 +0200
    Re: [PATCH] mutex: make mutex_lock_nested an inline function Peter Zijlstra <peterz@infradead.org> - 2015-10-14 10:30 +0200
      Re: [PATCH] mutex: make mutex_lock_nested an inline function Peter Zijlstra <peterz@infradead.org> - 2015-10-14 10:40 +0200
        Re: [PATCH] mutex: make mutex_lock_nested an inline function Arnd Bergmann <arnd@arndb.de> - 2015-10-14 11:10 +0200
          Re: [PATCH] mutex: make mutex_lock_nested an inline function Peter Zijlstra <peterz@infradead.org> - 2015-10-14 11:10 +0200
            Re: [PATCH] mutex: make mutex_lock_nested an inline function Mark Brown <broonie@kernel.org> - 2015-10-14 12:10 +0200
      Re: [PATCH] mutex: make mutex_lock_nested an inline function Mark Brown <broonie@kernel.org> - 2015-10-14 12:30 +0200
        Re: [PATCH] mutex: make mutex_lock_nested an inline function Peter Zijlstra <peterz@infradead.org> - 2015-10-14 13:10 +0200
          Re: [PATCH] mutex: make mutex_lock_nested an inline function Mark Brown <broonie@kernel.org> - 2015-10-14 14:40 +0200
            Re: [PATCH] mutex: make mutex_lock_nested an inline function Peter Zijlstra <peterz@infradead.org> - 2015-10-14 15:50 +0200
              Re: [PATCH] mutex: make mutex_lock_nested an inline function Peter Zijlstra <peterz@infradead.org> - 2015-10-14 16:00 +0200
                Re: [PATCH] mutex: make mutex_lock_nested an inline function Ingo Molnar <mingo@kernel.org> - 2015-10-14 16:00 +0200
              Re: [PATCH] mutex: make mutex_lock_nested an inline function Mark Brown <broonie@kernel.org> - 2015-10-14 16:20 +0200

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