Re: Regression in next with use printk_safe buffers in printk

[Peter Zijlstra]

On Wed, Feb 15, 2017 at 01:01:40AM +0900, Sergey Senozhatsky wrote:
> 
> but I'm a bit confused by rt_b->rt_runtime_lock in this unsafe lock
> scenario (so it's not ABBA, but ABAD)
> 
> >   lock(hrtimer_bases.lock);
> >                                lock(&rt_b->rt_runtime_lock);
> >                                lock(hrtimer_bases.lock);
> >   lock(tk_core);
> >
> >
> > Chain exists of:
> >
> >	tk_core --> &rt_b->rt_runtime_lock --> hrtimer_bases.lock
> 
> 
> I'm lacking some knowledge here, sorry. where does the tk_core --> &rt_b->rt_runtime_lock
> come from?

rt_b->rt_runtime_lock is one of the scheduler locks, since we do
printk() under tk_core, which does semaphore muck, which then includes
the entire scheduler chain of locks.