Re: [PATCH 13/14] lockdep: Implement lock pinning

[Ingo Molnar]

* Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> RFC: a possible alternative API would be something like:
> 
>   int cookie = lockdep_pin_lock(&foo);
>   ...
>   lockdep_unpin_lock(&foo, cookie);

Yeah, this would be even nicer.

> Where we pick a random number for the pin_count; this makes it
> impossible to sneak a lock break in without also passing the right
> cookie along.
> 
> I've not done this because it ends up generating code for !LOCKDEP,
> esp. if you need to pass the cookie around for some reason.

The cookie could be a zero-size structure, which can be 'passed around' 
syntactically but creates no overhead in the code.

But I'd expect cookie-passing to be a sign of badness in most cases: the lock 
should generally be unpinned at the same level of abstraction...

Thanks,

	Ingo
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