linux-kernel - Re: [PATCH v3 16/16] ARM: Remove custom IRQ stat accounting

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Message-ID: <875z83r08a.wl-maz@kernel.org>
Date:   Thu, 24 Sep 2020 10:29:57 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Guillaume Tucker <guillaume.tucker@...labora.com>
Cc:     Valentin Schneider <valentin.schneider@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Sumit Garg <sumit.garg@...aro.org>, kernel-team@...roid.com,
        Florian Fainelli <f.fainelli@...il.com>,
        Russell King <linux@....linux.org.uk>,
        Jason Cooper <jason@...edaemon.net>,
        Saravana Kannan <saravanak@...gle.com>,
        Andrew Lunn <andrew@...n.ch>,
        Catalin Marinas <catalin.marinas@....com>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, kernelci-results@...ups.io
Subject: Re: [PATCH v3 16/16] ARM: Remove custom IRQ stat accounting

Hi Guillaume,

On Thu, 24 Sep 2020 10:00:09 +0100,
Guillaume Tucker <guillaume.tucker@...labora.com> wrote:
> 
> Hi Marc,
> 
> On 01/09/2020 15:43, Marc Zyngier wrote:
> > Let's switch the arm code to the core accounting, which already
> > does everything we need.
> > 
> > Reviewed-by: Valentin Schneider <valentin.schneider@....com>
> > Signed-off-by: Marc Zyngier <maz@...nel.org>
> > ---
> >  arch/arm/include/asm/hardirq.h | 17 -----------------
> >  arch/arm/kernel/smp.c          | 20 ++++----------------
> >  2 files changed, 4 insertions(+), 33 deletions(-)
> 
> This appears to be causing a NULL pointer dereference on
> beaglebone-black, it got bisected automatically several times.
> None of the other platforms in the KernelCI labs appears to be
> affected.

Hmm. My bet is that because this is a UP machine running an SMP
kernel, and I fell into the trap of forgetting about this 32bit
configuration.

I expect the following patch to fix it. Please give it a go if you can
(I'm away at the moment and can't test much, and do not have any
physical 32bit machine to test this on).

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 00327fa74b01..b4e3d336dc33 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -531,7 +531,12 @@ void show_ipi_list(struct seq_file *p, int prec)
 	unsigned int cpu, i;
 
 	for (i = 0; i < NR_IPI; i++) {
-		unsigned int irq = irq_desc_get_irq(ipi_desc[i]);
+		unsigned int irq;
+
+		if (!ipi_desc[i])
+			continue;
+
+		irq = irq_desc_get_irq(ipi_desc[i]);
 		seq_printf(p, "%*s%u: ", prec - 1, "IPI", i);
 
 		for_each_online_cpu(cpu)

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.