linux-kernel - Re: WARNING: CPU: 0 PID: 0 at drivers/irqchip/irq-gic-v3-its.c

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Message-ID: <0e926f4b-1148-289b-39a1-ef76baa8cf9d@arm.com>
Date:   Fri, 9 Nov 2018 17:41:26 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     cai@....us, open list <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        ard.biesheuvel@...aro.org, Jason Cooper <jason@...edaemon.net>
Subject: Re: WARNING: CPU: 0 PID: 0 at drivers/irqchip/irq-gic-v3-its.c

On 09/11/18 17:28, Sudeep Holla wrote:
> On Fri, Nov 9, 2018 at 4:10 PM Marc Zyngier <marc.zyngier@....com> wrote:
>>
> [...]
> 
>>
>> See bb42ca474010 and d003d029cea8 for details.
>>
>> Now, activating this workaround leads to lockdep being really angry,
>> most likely because the cpus_read_lock is not taken, which is a change
>> in behaviour...
>>
>> I'm trying to dig into this now.
>>
> 
> Yes we found similar issue in kernel/sched/core.c sched_init_smp
> There's a fix with detailed description in -next
> (Commit 40fa3780bac2 ("sched/core: Take the hotplug lock in sched_init_smp()")
> 
> The behaviour changed since  commit cb538267ea1e ("jump_label/lockdep:
> Assert we hold the hotplug lock for _cpuslocked() operations")

I indeed came to the same conclusion, but the fix is slightly less than
obvious. I have the following arm64-specific crap, but it is pretty
terrible:

diff --git a/arch/arm64/kernel/time.c b/arch/arm64/kernel/time.c
index f258636273c9..9e96e9eaca9b 100644
--- a/arch/arm64/kernel/time.c
+++ b/arch/arm64/kernel/time.c
@@ -36,6 +36,7 @@
 #include <linux/clocksource.h>
 #include <linux/clk-provider.h>
 #include <linux/acpi.h>
+#include <linux/cpu.h>

 #include <clocksource/arm_arch_timer.h>

@@ -69,7 +70,9 @@ void __init time_init(void)
 	u32 arch_timer_rate;

 	of_clk_init(NULL);
+	cpus_read_lock();
 	timer_probe();
+	cpus_read_unlock();

 	tick_setup_hrtimer_broadcast();

Qian, can you please let me know if this helps? If it does, we'll have
to think of something a bit better...

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...