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

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Date:   Fri, 21 Feb 2020 21:25:11 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        mingo@...nel.org, joel@...lfernandes.org,
        gregkh@...uxfoundation.org, gustavo@...eddedor.com,
        tglx@...utronix.de, paulmck@...nel.org, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        luto@...nel.org, tony.luck@...el.com, frederic@...nel.org,
        dan.carpenter@...cle.com, mhiramat@...nel.org
Subject: Re: [PATCH v4 01/27] lockdep: Teach lockdep about "USED" <- "IN-NMI"
 inversions

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@...radead.org> 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)