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Date:   Mon, 12 Nov 2018 08:39:26 +0000
Message-ID: <86lg5yelkx.wl-marc.zyngier@arm.com>
From:   Marc Zyngier <marc.zyngier@arm.com>
To:     Qian Cai <cai@gmx.us>
Cc:     Sudeep Holla <sudeep.holla@arm.com>,
        open list <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Jason Cooper <jason@lakedaemon.net>
Subject: Re: WARNING: CPU: 0 PID: 0 at drivers/irqchip/irq-gic-v3-its.c
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On Fri, 09 Nov 2018 18:41:03 +0000,
Qian Cai <cai@gmx.us> wrote:
> 
> 
> 
> > On Nov 9, 2018, at 12:41 PM, Marc Zyngier <marc.zyngier@arm.com> wrote:
> > 
> > On 09/11/18 17:28, Sudeep Holla wrote:
> >> On Fri, Nov 9, 2018 at 4:10 PM Marc Zyngier <marc.zyngier@arm.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…
> After applied the above patch, the original warning is gone but there
> Is now a new warning.

[...]

Which was ful;ly expected, given that I've taken the cpu lock at some
semi-random location. I'll try to talk to PeterZ this week to try and
solve this.

Thanks,

	M.

-- 
Jazz is not dead, it just smell funny.