linux-kernel - Re: [PATCH v1 07/25] lockdep: Add preemption disabled assertion API

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Date:   Sat, 23 May 2020 16:59:42 +0200
From:   "Sebastian A. Siewior" <bigeasy@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 07/25] lockdep: Add preemption disabled assertion API

On 2020-05-22 19:55:03 [+0200], Peter Zijlstra wrote:
> On Tue, May 19, 2020 at 11:45:29PM +0200, Ahmed S. Darwish wrote:
> > diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> > index 206774ac6946..54c929ea5b98 100644
> > --- a/include/linux/lockdep.h
> > +++ b/include/linux/lockdep.h
> > @@ -702,6 +702,14 @@ do {									\
> >  			  "Not in hardirq as expected\n");		\
> >  	} while (0)
> >  
> > +/*
> > + * Don't define this assertion here to avoid a call-site's header file
> > + * dependency on sched.h task_struct current. This is needed by call
> > + * sites that are inline defined at header files already included by
> > + * sched.h.
> > + */
> > +void lockdep_assert_preemption_disabled(void);
> 
> So how about:
> 
> #if defined(CONFIG_PREEMPT_COUNT) && defined(CONFIG_TRACE_IRQFLAGS)
> #define lockdep_assert_preemption_disabled() do { \
> 		WARN_ON(debug_locks && !preempt_count() && \
> 			current->hardirqs_enabled); \
> 	} while (0)
> #else
> #define lockdep_assert_preemption_disabled() do { } while (0)
> #endif
> 
> That is both more consistent with the things you claim it's modelled
> after and also completely avoids that header dependency.

So we need additionally: 

- #include <linux/sched.h> in include/linux/flex_proportions.h
  and I think un another file as well.

- write_seqcount_t_begin_nested() as a define

- write_seqcount_t_begin() as a define

Any "static inline" in the header file using
lockdep_assert_preemption_disabled() will tro to complain about missing
current-> define. But yes, it will work otherwise.

Sebastian