[PATCH v4 7/8] lockdep: Change hardirq{s_enabled,_context} to per-cpu variables

[Ahmed S. Darwish]

On Tue, Jun 23, 2020 at 05:24:50PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 23, 2020 at 05:00:31PM +0200, Ahmed S. Darwish wrote:
> > On Tue, Jun 23, 2020 at 10:36:52AM +0200, Peter Zijlstra wrote:
> > ...
> > > -#define lockdep_assert_irqs_disabled()	do {				\
> > > -		WARN_ONCE(debug_locks && !current->lockdep_recursion &&	\
> > > -			  current->hardirqs_enabled,			\
> > > -			  "IRQs not disabled as expected\n");		\
> > > -	} while (0)
> > > +#define lockdep_assert_irqs_enabled()					\
> > > +do {									\
> > > +	WARN_ON_ONCE(debug_locks && !this_cpu_read(hardirqs_enabled));	\
> > > +} while (0)
> > >
> >
> > Can we add a small comment on top of lockdep_off(), stating that lockdep
> > IRQ tracking will still be kept after a lockdep_off call?
>
> That would only legitimize lockdep_off(). The only comment I want to put
> on that is: "if you use this, you're doing it wrong'.
>

Well, freshly merged code is using it. For example, KCSAN:

    => f1bc96210c6a ("kcsan: Make KCSAN compatible with lockdep")
    => kernel/kcsan/report.c:

    void kcsan_report(...)
    {
	...
        /*
         * With TRACE_IRQFLAGS, lockdep's IRQ trace state becomes corrupted if
         * we do not turn off lockdep here; this could happen due to recursion
         * into lockdep via KCSAN if we detect a race in utilities used by
         * lockdep.
         */
        lockdep_off();
	...
    }

thanks,

--
Ahmed S. Darwish
Linutronix GmbH