irqchip/sifive-plic: Chain to parent IRQ after handlers are ready

Now that the PLIC uses a platform driver, the driver is probed later in the
boot process, where interrupts from peripherals might already be pending.

As a result, plic_handle_irq() may be called as early as the call to
irq_set_chained_handler() completes. But this call happens before the
per-context handler is completely set up, so there is a window where
plic_handle_irq() can see incomplete per-context state and crash.

Avoid this by delaying the call to irq_set_chained_handler() until all
handlers from all PLICs are initialized.

Fixes: 8ec99b033147 ("irqchip/sifive-plic: Convert PLIC driver into a platform driver")
Reported-by: Geert Uytterhoeven <[e-mail]>
Signed-off-by: Samuel Holland <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Tested-by: Geert Uytterhoeven <[e-mail]>
Reviewed-by: Anup Patel <[e-mail]>
Cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Closes: https://lore.kernel.org/r/[e-mail]/

drivers/irqchip/irq-sifive-plic.c

···
 	struct plic_priv	*priv;
 };
 static int plic_parent_irq __ro_after_init;
-static bool plic_cpuhp_setup_done __ro_after_init;
+static bool plic_global_setup_done __ro_after_init;
 static DEFINE_PER_CPU(struct plic_handler, plic_handlers);
 
 static int plic_irq_set_type(struct irq_data *d, unsigned int type);
···
 	unsigned long plic_quirks = 0;
 	struct plic_handler *handler;
 	u32 nr_irqs, parent_hwirq;
-	struct irq_domain *domain;
 	struct plic_priv *priv;
 	irq_hw_number_t hwirq;
-	bool cpuhp_setup;
 
 	if (is_of_node(dev->fwnode)) {
 		const struct of_device_id *id;
···
 			continue;
 		}
 
-		/* Find parent domain and register chained handler */
-		domain = irq_find_matching_fwnode(riscv_get_intc_hwnode(), DOMAIN_BUS_ANY);
-		if (!plic_parent_irq && domain) {
-			plic_parent_irq = irq_create_mapping(domain, RV_IRQ_EXT);
-			if (plic_parent_irq)
-				irq_set_chained_handler(plic_parent_irq, plic_handle_irq);
-		}
-
 		/*
 		 * When running in M-mode we need to ignore the S-mode handler.
 		 * Here we assume it always comes later, but that might be a
···
 		goto fail_cleanup_contexts;
 
 	/*
-	 * We can have multiple PLIC instances so setup cpuhp state
+	 * We can have multiple PLIC instances so setup global state
 	 * and register syscore operations only once after context
 	 * handlers of all online CPUs are initialized.
 	 */
-	if (!plic_cpuhp_setup_done) {
-		cpuhp_setup = true;
+	if (!plic_global_setup_done) {
+		struct irq_domain *domain;
+		bool global_setup = true;
+
 		for_each_online_cpu(cpu) {
 			handler = per_cpu_ptr(&plic_handlers, cpu);
 			if (!handler->present) {
-				cpuhp_setup = false;
+				global_setup = false;
 				break;
 			}
 		}
-		if (cpuhp_setup) {
+
+		if (global_setup) {
+			/* Find parent domain and register chained handler */
+			domain = irq_find_matching_fwnode(riscv_get_intc_hwnode(), DOMAIN_BUS_ANY);
+			if (domain)
+				plic_parent_irq = irq_create_mapping(domain, RV_IRQ_EXT);
+			if (plic_parent_irq)
+				irq_set_chained_handler(plic_parent_irq, plic_handle_irq);
+
 			cpuhp_setup_state(CPUHP_AP_IRQ_SIFIVE_PLIC_STARTING,
 					  "irqchip/sifive/plic:starting",
 					  plic_starting_cpu, plic_dying_cpu);
 			register_syscore_ops(&plic_irq_syscore_ops);
-			plic_cpuhp_setup_done = true;
+			plic_global_setup_done = true;
 		}
 	}