Messages in this thread | | | Date | Tue, 12 Dec 2017 11:31:37 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] ARM: CPU hotplug: Delegate complete() to surviving CPU |
| |
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 <van.freenix@gmail.com> > > Reported-by: Russell King - ARM Linux <linux@armlinux.org.uk> > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > Tested-by: Tested-by: Fabio Estevam <fabio.estevam@nxp.com> > > 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 <linux@armlinux.org.uk> > > Cc: Ingo Molnar <mingo@kernel.org> > > Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org> > > Cc: Michal Hocko <mhocko@suse.com> > > Cc: Thomas Gleixner <tglx@linutronix.de> > > Cc: <linux-arm-kernel@lists.infradead.org> > > > > 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------------{= > - baruch@tkos.co.il - tel: +972.52.368.4656, http://www.tkos.co.il - >
| |