Re: [RFC 1/4] lockdep: additional lock specific information when dumping locks

Peter Zijlstra
2015-01-12T15:37:58Z

On Mon, Jan 12, 2015 at 10:12:38AM -0500, Sasha Levin wrote:
> The reason for my patch is simple:

That might have maybe been good changelog material?

> I'm fuzzing with hundreds of worker threads
> which at some point trigger a complete system lockup for some reason.
>
> When lockdep dumps the list of held locks it shows that pretty much every one
> of those threads is holding the lock which caused the lockup, which is incorrect
> because it considers locks in the process of getting acquired as "held".
>
> This is my solution to that issue. I wanted to know which one of the threads is
> really holding the lock rather than just waiting on it.
>
> Is there a better way to solve that problem?

Sure, think moar, if the accompanying stack trace is in the middle
of the blocking primitive, ignore the top held lock ;-)

Alternatively, make better/more use of lock_acquired() and track the
acquire vs acquired information in the held_lock (1 bit) and look at it
when printing.