Re: [PATCH 1/2] lockdep: improve current->(hard|soft)irqs_enabled synchronisation with actual irq state

Excerpts from Alexey Kardashevskiy's message of July 24, 2020 2:16 pm:

On 23/07/2020 23:11, Nicholas Piggin wrote:

quoted

Excerpts from Peter Zijlstra's message of July 23, 2020 9:40 pm:

quoted

On Thu, Jul 23, 2020 at 08:56:14PM +1000, Nicholas Piggin wrote:

quoted

diff --git a/arch/powerpc/include/asm/hw_irq.h b/arch/powerpc/include/asm/hw_irq.h
index 3a0db7b0b46e..35060be09073 100644
--- a/arch/powerpc/include/asm/hw_irq.h
+++ b/arch/powerpc/include/asm/hw_irq.h

@@ -200,17 +200,14 @@ static inline bool arch_irqs_disabled(void)
 #define powerpc_local_irq_pmu_save(flags)			\
 	 do {							\
 		raw_local_irq_pmu_save(flags);			\
-		trace_hardirqs_off();				\
+		if (!raw_irqs_disabled_flags(flags))		\
+			trace_hardirqs_off();			\
 	} while(0)
 #define powerpc_local_irq_pmu_restore(flags)			\
 	do {							\
-		if (raw_irqs_disabled_flags(flags)) {		\
-			raw_local_irq_pmu_restore(flags);	\
-			trace_hardirqs_off();			\
-		} else {					\
+		if (!raw_irqs_disabled_flags(flags))		\
 			trace_hardirqs_on();			\
-			raw_local_irq_pmu_restore(flags);	\
-		}						\
+		raw_local_irq_pmu_restore(flags);		\
 	} while(0)

You shouldn't be calling lockdep from NMI context!

After this patch it doesn't.

trace_hardirqs_on/off implementation appears to expect to be called in NMI 
context though, for some reason.

quoted

That is, I recently
added suport for that on x86:

  https://lkml.kernel.org/r/20200623083721.155449112@infradead.org
  https://lkml.kernel.org/r/20200623083721.216740948@infradead.org

But you need to be very careful on how you order things, as you can see
the above relies on preempt_count() already having been incremented with
NMI_MASK.

Hmm. My patch seems simpler.

And your patches fix my error while Peter's do not:


IRQs not enabled as expected
WARNING: CPU: 0 PID: 1377 at /home/aik/p/kernel/kernel/softirq.c:169
__local_bh_enable_ip+0x118/0x190

I think they would have needed some powerpc bits as well. But I don't
see a reason we can't merge my patches, at least they fix this case and
don't seem to make things worse in any way.

Thanks,
Nick