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

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Date:   Wed, 19 Aug 2020 17:32:50 +0200
From:   peterz@...radead.org
To:     Alexey Kardashevskiy <aik@...abs.ru>
Cc:     Nicholas Piggin <npiggin@...il.com>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH 1/2] lockdep: improve current->(hard|soft)irqs_enabled
 synchronisation with actual irq state

On Wed, Aug 19, 2020 at 08:39:13PM +1000, Alexey Kardashevskiy wrote:

> > or current upstream?
> 
> The upstream 18445bf405cb (13 hours old) also shows the problem. Yours
> 1/2 still fixes it.

Afaict that just reduces the window.

Isn't the problem that:

arch/powerpc/kernel/exceptions-64e.S

	START_EXCEPTION(perfmon);
	NORMAL_EXCEPTION_PROLOG(0x260, BOOKE_INTERRUPT_PERFORMANCE_MONITOR,
				PROLOG_ADDITION_NONE)
	EXCEPTION_COMMON(0x260)
	INTS_DISABLE
#	  RECONCILE_IRQ_STATE
#	    TRACE_DISABLE_INTS
#	      TRACE_WITH_FRAME_BUFFER(trace_hardirqs_off)
#
# but we haven't done nmi_enter() yet... whoopsy

	CHECK_NAPPING()
	addi	r3,r1,STACK_FRAME_OVERHEAD
	bl	performance_monitor_exception
#	 perf_irq()
#          perf_event_interrupt
#	     __perf_event_interrupt
#	      nmi_enter()



That is, afaict your entry code is buggered.