irqchip/mips: Fix RCU violation when using irqdomain lookup on interrupt entry

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.

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>
[maz: add dependency on CONFIG_IRQ_DOMAIN after report from the kernelci bot]
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
Link: https://lore.kernel.org/r/20210706110647.3979002-1-maz@kernel.org

2 files changed, 19 insertions, 0 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..d20e002b3246 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 +108,18 @@ void __irq_entry do_IRQ(unsigned int irq)
 	irq_exit();
 }
 
+#ifdef CONFIG_IRQ_DOMAIN
+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();
+}
+#endif