Re: [PATCH] irqchip/mips: Fix RCU violation when using irqdomain lookup on interrupt entry

Serge Semin
2021-07-08T09:46:16Z

Hi Marc,
Thanks for the fix.

On Tue, Jul 06, 2021 at 12:06:47PM +0100, Marc Zyngier wrote:
> Since d4a45c68dc81 ("irqdomain: Protect the linear revmap with RCU"),
> any irqdomain lookup requires the RCU read lock to be held.
>
> This assumes that the architecture code will be structured such as
> irq_enter() will be called *before* the interrupt is looked up
> in the irq domain. However, this isn't the case for MIPS, and a number
> of drivers are structured to do it the other way around when handling
> an interrupt in their root irqchip (secondary irqchips are OK by
> construction).
>
> This results in a RCU splat on a lockdep-enabled kernel when the kernel
> takes an interrupt from idle, as reported by Guenter Roeck.

Alas I am still on 5.12-rc4, so can't test it out at the moment. Soon
after getting further on the modern kernel version I'll give this
patch a try on my hw and send a report.

Regards
-Sergey

>
> Note that this could have fired previously if any driver had used
> tree-based irqdomain, which always had the RCU requirement.
>
> To solve this, provide a MIPS-specific helper (do_domain_IRQ())
> as the pendent of do_IRQ() that will do thing in the right order
> (and maybe save some cycles in the process).
>
> Ideally, MIPS would be moved over to using handle_domain_irq(),
> but that's much more ambitious.
>
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Tested-by: Guenter Roeck <linux@roeck-us.net>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> Cc: Serge Semin <fancer.lancer@gmail.com>
> Link: https://lore.kernel.org/r/20210705172352.GA56304@roeck-us.net
> ---
> arch/mips/include/asm/irq.h | 3 +++
> arch/mips/kernel/irq.c | 14 ++++++++++++++
> drivers/irqchip/irq-mips-cpu.c | 10 ++++++----
> drivers/irqchip/irq-mips-gic.c | 8 ++++----
> drivers/irqchip/irq-pic32-evic.c | 5 ++---
> 5 files changed, 29 insertions(+), 11 deletions(-)
>
> diff --git a/arch/mips/include/asm/irq.h b/arch/mips/include/asm/irq.h
> index d1477ecb1af9..57561e0e6e8d 100644
> --- a/arch/mips/include/asm/irq.h
> +++ b/arch/mips/include/asm/irq.h
> @@ -57,6 +57,9 @@ asmlinkage void plat_irq_dispatch(void);
>
> extern void do_IRQ(unsigned int irq);
>
> +struct irq_domain;
> +extern void do_domain_IRQ(struct irq_domain *domain, unsigned int irq);
> +
> extern void arch_init_irq(void);
> extern void spurious_interrupt(void);
>
> diff --git a/arch/mips/kernel/irq.c b/arch/mips/kernel/irq.c
> index 85b6c60f285d..c76005cd3b79 100644
> --- a/arch/mips/kernel/irq.c
> +++ b/arch/mips/kernel/irq.c
> @@ -21,6 +21,7 @@
> #include <linux/kallsyms.h>
> #include <linux/kgdb.h>
> #include <linux/ftrace.h>
> +#include <linux/irqdomain.h>
>
> #include <linux/atomic.h>
> #include <linux/uaccess.h>
> @@ -107,3 +108,16 @@ void __irq_entry do_IRQ(unsigned int irq)
> irq_exit();
> }
>
> +void __irq_entry do_domain_IRQ(struct irq_domain *domain, unsigned int hwirq)
> +{
> + struct irq_desc *desc;
> +
> + irq_enter();
> + check_stack_overflow();
> +
> + desc = irq_resolve_mapping(domain, hwirq);
> + if (likely(desc))
> + handle_irq_desc(desc);
> +
> + irq_exit();
> +}
> diff --git a/drivers/irqchip/irq-mips-cpu.c b/drivers/irqchip/irq-mips-cpu.c
> index 0bbb0b2d0dd5..0c7ae71a0af0 100644
> --- a/drivers/irqchip/irq-mips-cpu.c
> +++ b/drivers/irqchip/irq-mips-cpu.c
> @@ -127,7 +127,6 @@ static struct irq_chip mips_mt_cpu_irq_controller = {
> asmlinkage void __weak plat_irq_dispatch(void)
> {
> unsigned long pending = read_c0_cause() & read_c0_status() & ST0_IM;
> - unsigned int virq;
> int irq;
>
> if (!pending) {
> @@ -137,12 +136,15 @@ asmlinkage void __weak plat_irq_dispatch(void)
>
> pending >>= CAUSEB_IP;
> while (pending) {
> + struct irq_domain *d;
> +
> irq = fls(pending) - 1;
> if (IS_ENABLED(CONFIG_GENERIC_IRQ_IPI) && irq < 2)
> - virq = irq_linear_revmap(ipi_domain, irq);
> + d = ipi_domain;
> else
> - virq = irq_linear_revmap(irq_domain, irq);
> - do_IRQ(virq);
> + d = irq_domain;
> +
> + do_domain_IRQ(d, irq);
> pending &= ~BIT(irq);
> }
> }
> diff --git a/drivers/irqchip/irq-mips-gic.c b/drivers/irqchip/irq-mips-gic.c
> index b146e069bf5b..54c7092cc61d 100644
> --- a/drivers/irqchip/irq-mips-gic.c
> +++ b/drivers/irqchip/irq-mips-gic.c
> @@ -169,8 +169,8 @@ static void gic_handle_shared_int(bool chained)
> generic_handle_domain_irq(gic_irq_domain,
> GIC_SHARED_TO_HWIRQ(intr));
> else
> - do_IRQ(irq_find_mapping(gic_irq_domain,
> - GIC_SHARED_TO_HWIRQ(intr)));
> + do_domain_IRQ(gic_irq_domain,
> + GIC_SHARED_TO_HWIRQ(intr));
> }
> }
>
> @@ -320,8 +320,8 @@ static void gic_handle_local_int(bool chained)
> generic_handle_domain_irq(gic_irq_domain,
> GIC_LOCAL_TO_HWIRQ(intr));
> else
> - do_IRQ(irq_find_mapping(gic_irq_domain,
> - GIC_LOCAL_TO_HWIRQ(intr)));
> + do_domain_IRQ(gic_irq_domain,
> + GIC_LOCAL_TO_HWIRQ(intr));
> }
> }
>
> diff --git a/drivers/irqchip/irq-pic32-evic.c b/drivers/irqchip/irq-pic32-evic.c
> index 34c4b4ffacd1..1d9bb28d13e5 100644
> --- a/drivers/irqchip/irq-pic32-evic.c
> +++ b/drivers/irqchip/irq-pic32-evic.c
> @@ -42,11 +42,10 @@ static void __iomem *evic_base;
>
> asmlinkage void __weak plat_irq_dispatch(void)
> {
> - unsigned int irq, hwirq;
> + unsigned int hwirq;
>
> hwirq = readl(evic_base + REG_INTSTAT) & 0xFF;
> - irq = irq_linear_revmap(evic_irq_domain, hwirq);
> - do_IRQ(irq);
> + do_domain_IRQ(evic_irq_domain, hwirq);
> }
>
> static struct evic_chip_data *irqd_to_priv(struct irq_data *data)
> --
> 2.30.2
>