Re: [PATCH v4 01/27] lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions

[Peter Zijlstra]

On Fri, Feb 21, 2020 at 10:08:55AM -0500, Steven Rostedt wrote:
> On Fri, 21 Feb 2020 14:34:17 +0100
> Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 
> > --- a/kernel/locking/lockdep.c
> > +++ b/kernel/locking/lockdep.c
> > @@ -379,13 +379,13 @@ void lockdep_init_task(struct task_struc
> >  
> >  void lockdep_off(void)
> >  {
> > -	current->lockdep_recursion++;
> > +	current->lockdep_recursion += BIT(16);
> >  }
> >  EXPORT_SYMBOL(lockdep_off);
> >  
> >  void lockdep_on(void)
> >  {
> > -	current->lockdep_recursion--;
> > +	current->lockdep_recursion -= BIT(16);
> >  }
> >  EXPORT_SYMBOL(lockdep_on);
> >  
> 
> > +
> > +static bool lockdep_nmi(void)
> > +{
> > +	if (current->lockdep_recursion & 0xFFFF)
> 
> Nitpick, but the association with bit 16 and this mask really should be
> defined as a macro somewhere and not have hard coded numbers.

Right, I suppose I can do something like:

#define LOCKDEP_RECURSION_BITS	16
#define LOCKDEP_OFF (1U << LOCKDEP_RECURSION_BITS)
#define LOCKDEP_RECURSION_MASK (LOCKDEP_OFF - 1)