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Message-ID: <20230124225628.GZ2948950@paulmck-ThinkPad-P17-Gen-1> Date: Tue, 24 Jan 2023 14:56:28 -0800 From: "Paul E. McKenney" <paulmck@...nel.org> To: "Joel Fernandes (Google)" <joel@...lfernandes.org> Cc: linux-kernel@...r.kernel.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Frederic Weisbecker <frederic@...nel.org>, Zhouyi Zhou <zhouzhouyi@...il.com>, Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>, rcu <rcu@...r.kernel.org>, stable@...r.kernel.org, Frederic Weisbecker <fweisbec@...il.com>, Ingo Molnar <mingo@...nel.org>, "Rafael J. Wysocki" <rafael@...nel.org>, Thomas Gleixner <tglx@...utronix.de> Subject: Re: [PATCH v2 RESEND] tick/nohz: Fix cpu_is_hotpluggable() by checking with nohz subsystem On Tue, Jan 24, 2023 at 05:31:26PM +0000, Joel Fernandes (Google) wrote: > For CONFIG_NO_HZ_FULL systems, the tick_do_timer_cpu cannot be offlined. > However, cpu_is_hotpluggable() still returns true for those CPUs. This causes > torture tests that do offlining to end up trying to offline this CPU causing > test failures. Such failure happens on all architectures. > > Fix it by asking the opinion of the nohz subsystem on whether the CPU can > be hotplugged. > > [ Apply Frederic Weisbecker feedback on refactoring tick_nohz_cpu_down(). ] > > For drivers/base/ portion: > Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> > > Cc: Frederic Weisbecker <frederic@...nel.org> > Cc: "Paul E. McKenney" <paulmck@...nel.org> > Cc: Zhouyi Zhou <zhouzhouyi@...il.com> > Cc: Will Deacon <will@...nel.org> > Cc: Marc Zyngier <maz@...nel.org> > Cc: rcu <rcu@...r.kernel.org> > Cc: stable@...r.kernel.org > Fixes: 2987557f52b9 ("driver-core/cpu: Expose hotpluggability to the rest of the kernel") > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org> Queued for further review and testing, thank you both! It might be a few hours until it becomes publicly visible, but it will get there. Thanx, Paul > --- > Sorry, resending with CC to stable. > > drivers/base/cpu.c | 3 ++- > include/linux/tick.h | 2 ++ > kernel/time/tick-sched.c | 11 ++++++++--- > 3 files changed, 12 insertions(+), 4 deletions(-) > > diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c > index 55405ebf23ab..450dca235a2f 100644 > --- a/drivers/base/cpu.c > +++ b/drivers/base/cpu.c > @@ -487,7 +487,8 @@ static const struct attribute_group *cpu_root_attr_groups[] = { > bool cpu_is_hotpluggable(unsigned int cpu) > { > struct device *dev = get_cpu_device(cpu); > - return dev && container_of(dev, struct cpu, dev)->hotpluggable; > + return dev && container_of(dev, struct cpu, dev)->hotpluggable > + && tick_nohz_cpu_hotpluggable(cpu); > } > EXPORT_SYMBOL_GPL(cpu_is_hotpluggable); > > diff --git a/include/linux/tick.h b/include/linux/tick.h > index bfd571f18cfd..9459fef5b857 100644 > --- a/include/linux/tick.h > +++ b/include/linux/tick.h > @@ -216,6 +216,7 @@ extern void tick_nohz_dep_set_signal(struct task_struct *tsk, > enum tick_dep_bits bit); > extern void tick_nohz_dep_clear_signal(struct signal_struct *signal, > enum tick_dep_bits bit); > +extern bool tick_nohz_cpu_hotpluggable(unsigned int cpu); > > /* > * The below are tick_nohz_[set,clear]_dep() wrappers that optimize off-cases > @@ -280,6 +281,7 @@ static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask) { } > > static inline void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit) { } > static inline void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit) { } > +static inline bool tick_nohz_cpu_hotpluggable(unsigned int cpu) { return true; } > > static inline void tick_dep_set(enum tick_dep_bits bit) { } > static inline void tick_dep_clear(enum tick_dep_bits bit) { } > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index 9c6f661fb436..63e3e8ebcd64 100644 > --- a/kernel/time/tick-sched.c > +++ b/kernel/time/tick-sched.c > @@ -510,7 +510,7 @@ void __init tick_nohz_full_setup(cpumask_var_t cpumask) > tick_nohz_full_running = true; > } > > -static int tick_nohz_cpu_down(unsigned int cpu) > +bool tick_nohz_cpu_hotpluggable(unsigned int cpu) > { > /* > * The tick_do_timer_cpu CPU handles housekeeping duty (unbound > @@ -518,8 +518,13 @@ static int tick_nohz_cpu_down(unsigned int cpu) > * CPUs. It must remain online when nohz full is enabled. > */ > if (tick_nohz_full_running && tick_do_timer_cpu == cpu) > - return -EBUSY; > - return 0; > + return false; > + return true; > +} > + > +static int tick_nohz_cpu_down(unsigned int cpu) > +{ > + return tick_nohz_cpu_hotpluggable(cpu) ? 0 : -EBUSY; > } > > void __init tick_nohz_init(void) > -- > 2.39.1.405.gd4c25cc71f-goog >
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