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Re: + kernel-locking-lockdepc-make-lockdep-initialize-itself-on-demand.patch added to -mm tree

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* Andrew Morton <akpm@linux-foundation.org> wrote:

> > and it should happen in a well defined place, not be opportunistic (and 
> > relatively random) like this, making it dependent on config options and 
> > calling contexts.
> 
> That's an unusable assertion, sorry.
> 
> Initializing lockdep in the above manner guarantees that it is initialized 
> before it is used.  It is *much* more reliable than "try to initialize it before 
> some piece of code which hasn't even been written yet tries to take a lock".

So I didn't like that patch because it called into lockdep in a messy way, without 
having any real knowledge about whether it's safe to do. Should lockdep ever grow 
more complex initialization, such a solution could break in subtle ways. I prefer 
clearly broken code with static dependencies over context-dependent broken code 
with dynamic call ordering/dependencies.

Fortunately we don't have to apply the patch:

> The conceptual problem is that if some piece of code does spin_lock_init() or 
> DEFINE_SPINLOCK(), that lock isn't necessarily initialized yet.

The conceptual problem is that the data structures are not build time initialized 
- but the hlist conversion patch solves that problem nicely!

So I'm a happy camper.

Thanks,

	Ingo

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Re: +  kernel-locking-lockdepc-make-lockdep-initialize-itself-on-demand.patch added  to -mm tree Ingo Molnar <mingo@kernel.org> - 2016-02-03 08:50 +0100
  Re: +  kernel-locking-lockdepc-make-lockdep-initialize-itself-on-demand.patch added  to -mm tree Andrey Ryabinin <aryabinin@virtuozzo.com> - 2016-02-03 10:50 +0100
    Re: +  kernel-locking-lockdepc-make-lockdep-initialize-itself-on-demand.patch added  to -mm tree Ingo Molnar <mingo@kernel.org> - 2016-02-03 10:50 +0100
  Re: +  kernel-locking-lockdepc-make-lockdep-initialize-itself-on-demand.patch  added to -mm tree Andrew Morton <akpm@linux-foundation.org> - 2016-02-03 17:50 +0100
    Re: +  kernel-locking-lockdepc-make-lockdep-initialize-itself-on-demand.patch  added to -mm tree Andrew Morton <akpm@linux-foundation.org> - 2016-02-03 21:50 +0100
      Re: +  kernel-locking-lockdepc-make-lockdep-initialize-itself-on-demand.patch  added to -mm tree Andrew Morton <akpm@linux-foundation.org> - 2016-02-03 22:50 +0100
        Re: +  kernel-locking-lockdepc-make-lockdep-initialize-itself-on-demand.patch added  to -mm tree Andrey Ryabinin <aryabinin@virtuozzo.com> - 2016-02-04 14:20 +0100
          Re: +  kernel-locking-lockdepc-make-lockdep-initialize-itself-on-demand.patch  added to -mm tree Michael Ellerman <mpe@ellerman.id.au> - 2016-02-08 10:40 +0100
          Re: +  kernel-locking-lockdepc-make-lockdep-initialize-itself-on-demand.patch added  to -mm tree Ingo Molnar <mingo@kernel.org> - 2016-02-09 12:10 +0100
    Re: +  kernel-locking-lockdepc-make-lockdep-initialize-itself-on-demand.patch added  to -mm tree Ingo Molnar <mingo@kernel.org> - 2016-02-09 12:20 +0100
      Re: +  kernel-locking-lockdepc-make-lockdep-initialize-itself-on-demand.patch  added to -mm tree Andrew Morton <akpm@linux-foundation.org> - 2016-02-09 21:20 +0100

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