On Tue, Dec 12, 2017 at 07:40:46PM +0200, Baruch Siach wrote:
> Hi Paul,
>
> On Tue, Dec 12, 2017 at 09:20:59AM -0800, Paul E. McKenney wrote:
> > The ARM implementation of arch_cpu_idle_dead() invokes complete(), but
> > does so after RCU has stopped watching the outgoing CPU, which results
> > in lockdep complaints because complete() invokes functions containing RCU
> > readers. This patch therefore uses Thomas Gleixner's trick of delegating
> > the complete() call to a surviving CPU via smp_call_function_single().
> >
> > Reported-by: Peng Fan <[email protected]>
> > Reported-by: Russell King - ARM Linux <[email protected]>
> > Signed-off-by: Paul E. McKenney <[email protected]>
> > Tested-by: Tested-by: Fabio Estevam <[email protected]>
>
> Fabio reported only once, though he might have tested twice.
Actually, he did test twice. Apparently this patch has problems
with CONFIG_BL_SWITCHER=y kernels.
But yes, I guess I did get a bit carried away with the Tested-by's,
didn't I? ;-)
Thanx, Paul
> baruch
>
> > Cc: Russell King <[email protected]>
> > Cc: Ingo Molnar <[email protected]>
> > Cc: "Peter Zijlstra (Intel)" <[email protected]>
> > Cc: Michal Hocko <[email protected]>
> > Cc: Thomas Gleixner <[email protected]>
> > Cc: <[email protected]>
> >
> > diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> > index b4fbf00ee4ad..75f85e20aafa 100644
> > --- a/arch/arm/kernel/smp.c
> > +++ b/arch/arm/kernel/smp.c
> > @@ -267,6 +267,14 @@ void __cpu_die(unsigned int cpu)
> > }
> >
> > /*
> > + * Invoke complete() on behalf of the outgoing CPU.
> > + */
> > +static void arch_cpu_idle_dead_complete(void *arg)
> > +{
> > + complete(&cpu_died);
> > +}
> > +
> > +/*
> > * Called from the idle thread for the CPU which has been shutdown.
> > *
> > * Note that we disable IRQs here, but do not re-enable them
> > @@ -293,9 +301,11 @@ void arch_cpu_idle_dead(void)
> > /*
> > * Tell __cpu_die() that this CPU is now safe to dispose of. Once
> > * this returns, power and/or clocks can be removed at any point
> > - * from this CPU and its cache by platform_cpu_kill().
> > + * from this CPU and its cache by platform_cpu_kill(). We cannot
> > + * call complete() this late, so we delegate it to an online CPU.
> > */
> > - complete(&cpu_died);
> > + smp_call_function_single(cpumask_first(cpu_online_mask),
> > + arch_cpu_idle_dead_complete, NULL, 0);
> >
> > /*
> > * Ensure that the cache lines associated with that completion are
>
> --
> http://baruch.siach.name/blog/ ~. .~ Tk Open Systems
> =}------------------------------------------------ooO--U--Ooo------------{=
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