On Fri, Sep 08, 2023 at 10:35:59PM +0200, Frederic Weisbecker wrote: > rcu_report_dead() has to be called locally by the CPU that is going to > exit the RCU state machine. Passing a cpu argument here is error-prone > and leaves the possibility for a racy remote call. > > Use local access instead. > > Signed-off-by: Frederic Weisbecker <[email protected]>
I was going to ask for an assertion for "cpu" in cpu_die_early(), but given that its value comes from smp_processor_id() just a few lines earlier, there isn't a whole lot of point to that. So: Reviewed-by: Paul E. McKenney <[email protected]> > --- > arch/arm64/kernel/smp.c | 2 +- > include/linux/rcupdate.h | 2 +- > kernel/cpu.c | 2 +- > kernel/rcu/tree.c | 4 ++-- > 4 files changed, 5 insertions(+), 5 deletions(-) > > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c > index edd63894d61e..ce672cb69f1c 100644 > --- a/arch/arm64/kernel/smp.c > +++ b/arch/arm64/kernel/smp.c > @@ -401,7 +401,7 @@ void __noreturn cpu_die_early(void) > > /* Mark this CPU absent */ > set_cpu_present(cpu, 0); > - rcu_report_dead(cpu); > + rcu_report_dead(); > > if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) { > update_cpu_boot_status(CPU_KILL_ME); > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > index 5e5f920ade90..aa351ddcbe8d 100644 > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -122,7 +122,7 @@ static inline void call_rcu_hurry(struct rcu_head *head, > rcu_callback_t func) > void rcu_init(void); > extern int rcu_scheduler_active; > void rcu_sched_clock_irq(int user); > -void rcu_report_dead(unsigned int cpu); > +void rcu_report_dead(void); > void rcutree_migrate_callbacks(int cpu); > > #ifdef CONFIG_TASKS_RCU_GENERIC > diff --git a/kernel/cpu.c b/kernel/cpu.c > index 88a7ede322bd..86f08eafbd9f 100644 > --- a/kernel/cpu.c > +++ b/kernel/cpu.c > @@ -1368,7 +1368,7 @@ void cpuhp_report_idle_dead(void) > struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state); > > BUG_ON(st->state != CPUHP_AP_OFFLINE); > - rcu_report_dead(smp_processor_id()); > + rcu_report_dead(); > st->state = CPUHP_AP_IDLE_DEAD; > /* > * We cannot call complete after rcu_report_dead() so we delegate it > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 8b5ebef32e17..289c51417cbc 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -4551,11 +4551,11 @@ void rcu_cpu_starting(unsigned int cpu) > * from the outgoing CPU rather than from the cpuhp_step mechanism. > * This is because this function must be invoked at a precise location. > */ > -void rcu_report_dead(unsigned int cpu) > +void rcu_report_dead(void) > { > unsigned long flags; > unsigned long mask; > - struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); > + struct rcu_data *rdp = this_cpu_ptr(&rcu_data); > struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */ > > /* > -- > 2.41.0 >
