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

Ahmed S. Darwish
2020-05-26T00:53:09Z

Peter Zijlstra <peterz@infradead.org> wrote:
> On Sun, May 24, 2020 at 12:41:32AM +0200, Peter Zijlstra wrote:
> > On Sat, May 23, 2020 at 04:59:42PM +0200, Sebastian A. Siewior wrote:
> > >
> > > 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.
> >
> > Because...? /me rummages around.. Ah you're proposing sticking this in
> > seqcount itself and then header hell.
> >
> > Moo.. ok I'll go have another look on Monday.
>
> How's this?
>

This will work for my case as current-> is no longer referenced by the
lockdep macros. Please continue below though.

...

> -#define lockdep_assert_irqs_enabled() do { \
> - WARN_ONCE(debug_locks && !current->lockdep_recursion && \
> - !current->hardirqs_enabled, \
> - "IRQs not enabled as expected\n"); \
> - } while (0)
> +DECLARE_PER_CPU(int, hardirqs_enabled);
> +DECLARE_PER_CPU(int, hardirq_context);
>
> -#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)
>

Given that lockdep_off() is defined at lockdep.c as:

void lockdep_off(void)
{
current->lockdep_recursion += LOCKDEP_OFF;
}

This would imply that all of the macros:

- lockdep_assert_irqs_enabled()
- lockdep_assert_irqs_disabled()
- lockdep_assert_in_irq()
- lockdep_assert_preemption_disabled()
- lockdep_assert_preemption_enabled()

will do the lockdep checks *even if* lockdep_off() was called.

This doesn't sound right. Even if all of the above macros call sites
didn't care about lockdep_off()/on(), it is semantically incoherent.

Thanks,

--
Ahmed S. Darwish
Linutronix GmbH