Messages in this thread | | | Date | Tue, 19 May 2020 23:24:47 +0100 | From | Russell King - ARM Linux admin <> | Subject | Re: [PATCH 04/11] ARM: Allow IPIs to be handled as normal interrupts |
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On Tue, May 19, 2020 at 05:17:48PM +0100, Marc Zyngier wrote: > In order to deal with IPIs as normal interrupts, let's add > a new way to register them with the architecture code. > > set_smp_ipi_range() takes a range of interrupts, and allows > the arch code to request them as if the were normal interrupts. > A standard handler is then called by the core IRQ code to deal > with the IPI. > > This means that we don't need to call irq_enter/irq_exit, and > that we don't need to deal with set_irq_regs either. So let's > move the dispatcher into its own function, and leave handle_IPI() > as a compatibility function. > > On the sending side, let's make use of ipi_send_mask, which > already exists for this purpose.
You say nothing about the nesting of irq_enter() and irq_exit() for scheduler_ipi().
Given that lockdep introduced the requirement that hard IRQs can't be nested, are we sure that calling irq_exit() twice is safe?
Looking at irqtime_account_irq(), it seems that will cause double- accounting of in-interrupt time, since we will increment irq_start_time by just over twice the the period spent handling the IPI.
I think the rest of irq_exit() should be safe, but still, this behaviour should be documented at the very least, if not avoided.
> > Signed-off-by: Marc Zyngier <maz@kernel.org> > --- > arch/arm/Kconfig | 1 + > arch/arm/include/asm/smp.h | 5 ++ > arch/arm/kernel/smp.c | 97 ++++++++++++++++++++++++++++++++------ > 3 files changed, 88 insertions(+), 15 deletions(-) > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig > index c77c93c485a0..0caaba9bf880 100644 > --- a/arch/arm/Kconfig > +++ b/arch/arm/Kconfig > @@ -48,6 +48,7 @@ config ARM > select GENERIC_ARCH_TOPOLOGY if ARM_CPU_TOPOLOGY > select GENERIC_ATOMIC64 if CPU_V7M || CPU_V6 || !CPU_32v6K || !AEABI > select GENERIC_CLOCKEVENTS_BROADCAST if SMP > + select GENERIC_IRQ_IPI if SMP > select GENERIC_CPU_AUTOPROBE > select GENERIC_EARLY_IOREMAP > select GENERIC_IDLE_POLL_SETUP > diff --git a/arch/arm/include/asm/smp.h b/arch/arm/include/asm/smp.h > index a91f21e3c5b5..0e29730295ca 100644 > --- a/arch/arm/include/asm/smp.h > +++ b/arch/arm/include/asm/smp.h > @@ -45,6 +45,11 @@ extern void smp_init_cpus(void); > */ > extern void set_smp_cross_call(void (*)(const struct cpumask *, unsigned int)); > > +/* > + * Register IPI interrupts with the arch SMP code > + */ > +extern void set_smp_ipi_range(int ipi_base, int nr_ipi); > + > /* > * Called from platform specific assembly code, this is the > * secondary CPU entry point. > diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c > index 46e1be9e57a8..618641978a5b 100644 > --- a/arch/arm/kernel/smp.c > +++ b/arch/arm/kernel/smp.c > @@ -79,10 +79,19 @@ enum ipi_msg_type { > */ > }; > > +static int ipi_irq_base; > +static int nr_ipi = NR_IPI; > +static struct irq_desc *ipi_desc[NR_IPI]; > + > +static void ipi_setup(int cpu); > +static void ipi_teardown(int cpu); > + > static DECLARE_COMPLETION(cpu_running); > > static struct smp_operations smp_ops __ro_after_init; > > +static void ipi_setup(int cpu); > + > void __init smp_set_ops(const struct smp_operations *ops) > { > if (ops) > @@ -308,6 +317,8 @@ void arch_cpu_idle_dead(void) > > local_irq_disable(); > > + ipi_teardown(cpu); > + > /* > * Flush the data out of the L1 cache for this CPU. This must be > * before the completion to ensure that data is safely written out > @@ -424,6 +435,8 @@ asmlinkage void secondary_start_kernel(void) > > notify_cpu_starting(cpu); > > + ipi_setup(cpu); > + > calibrate_delay(); > > smp_store_cpu_info(cpu); > @@ -629,10 +642,9 @@ asmlinkage void __exception_irq_entry do_IPI(int ipinr, struct pt_regs *regs) > handle_IPI(ipinr, regs); > } > > -void handle_IPI(int ipinr, struct pt_regs *regs) > +static void do_handle_IPI(int ipinr) > { > unsigned int cpu = smp_processor_id(); > - struct pt_regs *old_regs = set_irq_regs(regs); > > if ((unsigned)ipinr < NR_IPI) { > trace_ipi_entry_rcuidle(ipi_types[ipinr]); > @@ -645,9 +657,7 @@ void handle_IPI(int ipinr, struct pt_regs *regs) > > #ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST > case IPI_TIMER: > - irq_enter(); > tick_receive_broadcast(); > - irq_exit(); > break; > #endif > > @@ -656,36 +666,26 @@ void handle_IPI(int ipinr, struct pt_regs *regs) > break; > > case IPI_CALL_FUNC: > - irq_enter(); > generic_smp_call_function_interrupt(); > - irq_exit(); > break; > > case IPI_CPU_STOP: > - irq_enter(); > ipi_cpu_stop(cpu); > - irq_exit(); > break; > > #ifdef CONFIG_IRQ_WORK > case IPI_IRQ_WORK: > - irq_enter(); > irq_work_run(); > - irq_exit(); > break; > #endif > > case IPI_COMPLETION: > - irq_enter(); > ipi_complete(cpu); > - irq_exit(); > break; > > case IPI_CPU_BACKTRACE: > printk_nmi_enter(); > - irq_enter(); > - nmi_cpu_backtrace(regs); > - irq_exit(); > + nmi_cpu_backtrace(get_irq_regs()); > printk_nmi_exit(); > break; > > @@ -697,9 +697,76 @@ void handle_IPI(int ipinr, struct pt_regs *regs) > > if ((unsigned)ipinr < NR_IPI) > trace_ipi_exit_rcuidle(ipi_types[ipinr]); > +} > + > +/* Legacy version, should go away once all irqchips have been converted */ > +void handle_IPI(int ipinr, struct pt_regs *regs) > +{ > + struct pt_regs *old_regs = set_irq_regs(regs); > + > + irq_enter(); > + do_handle_IPI(ipinr); > + irq_exit(); > + > set_irq_regs(old_regs); > } > > +static irqreturn_t ipi_handler(int irq, void *data) > +{ > + do_handle_IPI(irq - ipi_irq_base); > + return IRQ_HANDLED; > +} > + > +static void ipi_send(const struct cpumask *target, unsigned int ipi) > +{ > + __ipi_send_mask(ipi_desc[ipi], target); > +} > + > +static void ipi_setup(int cpu) > +{ > + if (ipi_irq_base) { > + int i; > + > + for (i = 0; i < nr_ipi; i++) > + enable_percpu_irq(ipi_irq_base + i, 0); > + } > +} > + > +static void ipi_teardown(int cpu) > +{ > + if (ipi_irq_base) { > + int i; > + > + for (i = 0; i < nr_ipi; i++) > + disable_percpu_irq(ipi_irq_base + i); > + } > +} > + > +void __init set_smp_ipi_range(int ipi_base, int n) > +{ > + int i; > + > + WARN_ON(n < NR_IPI); > + nr_ipi = min(n, NR_IPI); > + > + for (i = 0; i < nr_ipi; i++) { > + int err; > + > + err = request_percpu_irq(ipi_base + i, ipi_handler, > + "IPI", &irq_stat); > + WARN_ON(err); > + > + ipi_desc[i] = irq_to_desc(ipi_base + i); > + irq_set_status_flags(ipi_base + i, IRQ_NO_ACCOUNTING); > + } > + > + ipi_irq_base = ipi_base; > + set_smp_cross_call(ipi_send); > + > + /* Setup the boot CPU immediately */ > + ipi_setup(smp_processor_id()); > +} > + > void smp_send_reschedule(int cpu) > { > smp_cross_call(cpumask_of(cpu), IPI_RESCHEDULE); > -- > 2.26.2 > >
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